media: xc4000: don't ignore error if hwmodel fails

If, for some reason, reading the hwmodel register on
xc4000 fails, it will cause the following logig to
use a random value, as reported by smatch:

	drivers/media/tuners/xc4000.c:1047 check_firmware() error: uninitialized symbol 'hwmodel'.
	drivers/media/tuners/xc4000.c:1060 check_firmware() error: uninitialized symbol 'hwmodel'.
	drivers/media/tuners/xc4000.c:1064 check_firmware() error: uninitialized symbol 'hwmodel'.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>