compat-wireless: add sched.h on libertas/firmware.c

compat-wireless: add sched.h on libertas/firmware.c

sched.h is required to compile users of wake_up(),
firmware.c somehow gets sched.h included on newer kernels
but on older kernels this is not happening so include
this on the file itself. This patch should and will
be sent upstream.

This fixes this compilation error:

/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c: In function ‘lbs_fw_loaded’:
/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c:26:29: error: ‘TASK_NORMAL’ undeclared (first use in this function)
/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c:26:29: note: each undeclared identifier is reported only once for each function it appears in
/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c: In function ‘lbs_wait_for_firmware_load’:
/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c:110:260: error: ‘TASK_UNINTERRUPTIBLE’ undeclared (first use in this function)
/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.c:110:2: error: implicit declaration of function ‘schedule’ [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors

make[4]: *** [/home/mcgrof/devel/compat-wireless/drivers/net/wireless/libertas/firmware.o] Error 1

Signed-off-by: Luis R. Rodriguez <mcgrof@frijolero.org>