kernel: generic: 5.4: fix mips command line parameter patch

kernel: generic: 5.4: fix mips command line parameter patch

Fixing a build error when CONFIG_KERNEL_KEXEC is enabled:

make[5]: Entering directory '/home/bjorn/tmp/tmp-lede/build_dir/target-mipsel_24kc_musl/linux-ramips_mt7621/linux-5.4.28'
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  CHK     include/generated/compile.h
  CC      arch/mips/kernel/machine_kexec.o
arch/mips/kernel/machine_kexec.c: In function 'kexec_nonboot_cpu_jump':
arch/mips/kernel/machine_kexec.c:268:27: error: 'relocate_new_kernel_size' undeclared (first use in this function); did you mean 'kexec_relocate_new_kernel_end'?
      reboot_code_buffer + relocate_new_kernel_size);
                           ^~~~~~~~~~~~~~~~~~~~~~~~
                           kexec_relocate_new_kernel_end
arch/mips/kernel/machine_kexec.c:268:27: note: each undeclared identifier is reported only once for each function it appears in
arch/mips/kernel/machine_kexec.c: In function 'kexec_reboot':
arch/mips/kernel/machine_kexec.c:306:27: error: 'relocate_new_kernel_size' undeclared (first use in this function); did you mean 'kexec_relocate_new_kernel_end'?
      reboot_code_buffer + relocate_new_kernel_size);
                           ^~~~~~~~~~~~~~~~~~~~~~~~
                           kexec_relocate_new_kernel_end
make[7]: *** [scripts/Makefile.build:266: arch/mips/kernel/machine_kexec.o] Error 1

Signed-off-by: Bjørn Mork <bjorn@mork.no>