media: atomisp: Refactor atomisp_adjust_fmt()

Refactor atomisp_adjust_fmt():

1. The block starting at "format_bridge = atomisp_get_format_bridge(...)"
and ending with "if (field == V4L2_FIELD_ANY) field = V4L2_FIELD_NONE;"
is duplicated. With only the second block:
a) Properly checking that format_bridge is not NULL; amd
b) Having the special handling for IA_CSS_FRAME_FORMAT_RAW

Remove the first block.

2. On a NULL return from atomisp_get_format_bridge(f->fmt.pix.pixelformat)
fall back to V4L2_PIX_FMT_YUV420 just like in the IA_CSS_FRAME_FORMAT_RAW
case. atomisp_adjust_fmt() is used in VIDIOC_TRY_FMT handling and that
should jusy pick a fmt rather then returning -EINVAL.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>