[media] DaVinci-VPFE-Capture: Delete an unnecessary variable initialisation in vpfe_probe()

* Return an error code as a constant after a failed call of
  the function "vpfe_initialize".

* The local variable "ret" will be set then to an appropriate value
  a bit later. Thus omit the explicit initialisation at the beginning.

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>