reservation: Remove shadowing local variable 'ret'

commit 4eb2440ed60fb5793f7aa6da89b3d517cc59de43 upstream.

It was causing the return value of fence_is_signaled to be ignored, making
reservation objects signal too early.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>