media: imx: capture: Simplify __capture_legacy_try_fmt()

The __capture_legacy_try_fmt() function returns two values through
pointer arguments. One is a compose rectangle, which duplicates
informationr returned through the subdev format argument, and can thus
be removed. The other is the imx_media_pixfmt, which can be returned
by value instead.

Simplify the implementation of __capture_legacy_try_fmt() by dropping
the retcc and compose arguments, and returning the imx_media_pixfmt by
value.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>