media: pwc-ctl: pChoose can't be NULL

The way the code works, compression will be a valid value (less or equal to 3)
on both set_video_mode_foo() calls at the beginning of the while() loop.

So, the value for pChoose can't be NULL.

Solves those smatch warnings:

	drivers/media/usb/pwc/pwc-ctrl.c: drivers/media/usb/pwc/pwc-ctrl.c:252 set_video_mode_Timon() warn: variable dereferenced before check 'pChoose' (see line 248)
	drivers/media/usb/pwc/pwc-ctrl.c: drivers/media/usb/pwc/pwc-ctrl.c:302 set_video_mode_Kiara() warn: variable dereferenced before check 'pChoose' (see line 298)

and simplifies the code a little bit.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>