drm/etnaviv: fix missing unlock on error in etnaviv_gpu_submit()

drm/etnaviv: fix missing unlock on error in etnaviv_gpu_submit()

BugLink: http://bugs.launchpad.net/bugs/1687045
commit 45abdf35cf82e4270328c7237e7812de960ac560 upstream.

Add the missing unlock before return from function etnaviv_gpu_submit()
in the error handling case.

lst: fixed label name.

Fixes: f3cd1b064f11 ("drm/etnaviv: (re-)protect fence allocation with GPU mutex")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>