kernel: ltq-vmmc: fix compilation warning

kernel: ltq-vmmc: fix compilation warning

Fix compilation warning from ret not handled from copy_from_user and
missing fallthrough.
Fix compilation warning:
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_bbd.c: In function 'vmmc_BBD_WhiteListedCmdWr':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_bbd.c:1012:16: error: this statement may fall through [-Werror=implicit-fallthrough=]
 1012 |             if (IFX_TRUE == pCh->pParent->bSlicSupportsIdleMode)
      |                ^
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_bbd.c:1028:7: note: here
 1028 |       case VMMC_WL_SDD_RING_CFG:
      |       ^~~~
cc1: all warnings being treated as errors

/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_ioctl.c: In function 'VMMC_Dev_Spec_Ioctl':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_ioctl.c:111:15: error: ignoring return value of 'copy_from_user' declared with attribute 'warn_unused_result' [-Werror=unused-result]
  111 |               copy_from_user (p_arg, (IFX_uint8_t*)ioarg, sizeof(arg));\
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_ioctl.c:475:7: note: in expansion of macro 'ON_IOCTL'
  475 |       ON_IOCTL((VMMC_CHANNEL *) pLLDummyCh,
      |       ^~~~~~~~
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_ioctl.c:113:15: error: ignoring return value of 'copy_to_user' declared with attribute 'warn_unused_result' [-Werror=unused-result]
  113 |               copy_to_user ((IFX_uint8_t*)ioarg, p_arg, sizeof(arg));\
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xway/drv_vmmc-1.9.0/src/drv_vmmc_ioctl.c:475:7: note: in expansion of macro 'ON_IOCTL'
  475 |       ON_IOCTL((VMMC_CHANNEL *) pLLDummyCh,
      |       ^~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>