drm/i915: Fix runtime pm handling in i915_gem_shrink

We forgot to call intel_runtime_pm_put on error, fix it!

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: cf41a8f1

 ("drm/i915: Finally remove obj->mm.lock.")
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v5.13+
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210830121006.2978297-9-maarten.lankhorst@linux.intel.com
(cherry picked from commit 239f3c2e

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>