drm/i915: Initialize the obj flags for shmem objects

Obj flags for shmem objects is not being set correctly. Fixes in setting
BO_ALLOC_USER flag which applies to shmem objs as well.

v2: Add fixes tag (Tvrtko, Matt A)

Fixes: 13d29c82 ("drm/i915/ehl: unconditionally flush the pages on acquire")
Cc: <stable@vger.kernel.org> # v5.15+
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
[tursulin: Grouped all tags together.]
Link: https://patchwork.freedesktop.org/patch/msgid/20230203135205.4051149-1-aravind.iddamsetty@intel.com