staging: media: imx: remove temporary variable

Remove unnecessary local variable `ret` in file `imx6-mipi-csi2.c` and
directly returning the value assigned to `ret.`

Signed-off-by: Kaaira Gupta <kgupta@es.iitr.ac.in>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Link: https://lore.kernel.org/r/20200313215406.2485-3-kgupta@es.iitr.ac.in


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>