drm: Add missing __user annotation to drm_syncobj_array_find()

drm: Add missing __user annotation to drm_syncobj_array_find()

'user_handles' needs a __user annotation for fix the following sparse
warning:
drm_syncobj.c:813:37: warning: incorrect type in argument 2 (different address spaces)
drm_syncobj.c:813:37:    expected void const [noderef] <asn:1>*from
drm_syncobj.c:813:37:    got void *user_handles
drm_syncobj.c:875:38: warning: incorrect type in argument 2 (different address spaces)
drm_syncobj.c:875:38:    expected void *user_handles
drm_syncobj.c:875:38:    got void [noderef] <asn:1>*<noident>
drm_syncobj.c:908:38: warning: incorrect type in argument 2 (different address spaces)
drm_syncobj.c:908:38:    expected void *user_handles
drm_syncobj.c:908:38:    got void [noderef] <asn:1>*<noident>
drm_syncobj.c:941:38: warning: incorrect type in argument 2 (different address spaces)
drm_syncobj.c:941:38:    expected void *user_handles
drm_syncobj.c:941:38:    got void [noderef] <asn:1>*<noident>

Cc: Jason Ekstrand <jason@jlekstrand.net>
Fixes: 3e6fb72d6cef ("drm/syncobj: Add a syncobj_array_find helper")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170901165328.24459-2-ville.syrjala@linux.intel.com
Reviewed-by: Thierry Reding <treding@nvidia.com>