media: staging/intel-ipu3: Fix race condition during set_fmt

Do not modify imgu_pipe->nodes[inode].vdev_fmt.fmt.pix_mp, until the
format has been correctly validated.

Otherwise, even if we use a backup variable, there is a period of time
where imgu_pipe->nodes[inode].vdev_fmt.fmt.pix_mp might have an invalid
value that can be used by other functions.

Cc: stable@vger.kernel.org
Fixes: ad918499 ("media: staging/intel-ipu3: Fix set_fmt error handling")
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>