drm/msm: return -EFAULT if copy_from_user() fails

copy_from_user_inatomic() is actually a local function that returns
-EFAULT or positive values on error.  Otherwise copy_from_user() returns
the number of bytes remaining to be copied.  We want to return -EFAULT
here.

I removed an unlikely() because we just did a copy_from_user()
so I don't think it can possibly make a difference.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>