[media] DaVinci-VPFE-Capture: Move two assignments in vpfe_s_input()

Move assignments for two local variables into an else branch so that
their setting will only be performed after corresponding data processing
succeeded by this function.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>