iris: Fix return of iris_wait_syncobj()

iris_wait_syncobj() succeed if IOCTL return is 0 otherwise it failled.

Cc: mesa-stable
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <mesa/mesa!27500>
(cherry picked from commit 138303fb)