[media] am437x-vpfe: always assign bpp variable

[media] am437x-vpfe: always assign bpp variable

In vpfe_s_fmt(), when the sensor format and the requested format were
the same, bpp was assigned to vpfe->bpp without being initialized first.

Grab the bpp value that is currently used by using __vpfe_get_format()
instead of its wrapper, vpfe_try_fmt().

This use of uninitialized variable has been found by compiling the
kernel with clang.

Fixes: 417d2e507edc ("[media] media: platform: add VPFE capture driver
support for AM437X")

Cc: stable@vger.kernel.org
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>