media: imx214: don't de-reference a NULL pointer

As warned by smatch:
	drivers/media/i2c/imx214.c:591 imx214_set_format() warn: variable dereferenced before check 'format' (see line 589)

It turns that the code at imx214_set_format() has support for being
called with the format being NULL. I've no idea why, as it is only
called internally with the pointer set, and via subdev API (with
should also set it).

Also, the entire logic there depends on having format != NULL, so
just remove the bogus broken support for a null format.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>