msm: kgsl: Correctly use the return value of copy_to_user

copy_to_user() returns the number of bytes that were not copied
for whatever reason and *not* a error code.  Several areas of
the code are blindly returning the value of copy_to_user() which
could result in some mistaken assumptions down the road.

Change-Id: Ic0dedbade40248c46b7b8d2b18420b7612492b65
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>