[media] staging: davinci_vpfe: fix error check

The check would check the pointer, which is never less than 0.
According to the error message, the correct check would be
to check the return value of ipipe_mode. Check that instead.

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Levente Kurusa <levex@linux.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>