drm/shmem-helper: Remove another errant put in error path

drm/shmem-helper: Remove another errant put in error path

commit 3244422541603df9ddc56c40a70330df86aa5d4f upstream.

drm_gem_shmem_mmap() doesn't own reference in error code path, resulting
in the dma-buf shmem GEM object getting prematurely freed leading to a
later use-after-free.

Fixes: 4ed95f7c9dbd ("drm/shme-helpers: Fix dma_buf_mmap forwarding bug")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230108211311.3950107-1-dmitry.osipenko@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>