gpu: ion: Ensure ioctl return correct error codes

Under certain error conditions the following ION ioctl's would return
success even when the operation failed:

-ION_IOC_CLEAN_CACHES
-ION_IOC_INV_CACHES
-ION_IOC_CLEAN_INV_CACHES

Add return of correct error codes when an error occurs.

Change-Id: Ie8824bfecbb423c23d32c6a3d7058f06d8322906
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>