staging: bcm2835-audio: propagate PTR_ERR value instead of -EPERM

It is better to propagate PTR_ERR value instead of a hardcoded value
(-EPERM here)

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>