staging: mmal-vchiq: If the VPU returns an error, don't negate it

staging: mmal-vchiq: If the VPU returns an error, don't negate it

There is an enum for the errors that the VPU can return.
port_parameter_get was negating that value, but also using -EINVAL
from the Linux error codes.
Pass the VPU error code as positive values. Should the function
need to pass a Linux failure, then return that as negative.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20200629150945.10720-7-nsaenzjulienne@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>