drm/i915/gem: add missing else

Add missing else in set_proto_ctx_param() to fix coverity issue.

Addresses-Coverity: ("Unused value")
Fixes: d4433c76 ("drm/i915/gem: Use the proto-context to handle create parameters (v5)")
Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: katrinzhou <katrinzhou@tencent.com>
[tursulin: fixup alignment]
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220621124926.615884-1-tvrtko.ursulin@linux.intel.com