egl/dri2: Don't check return result of mtx_unlock().

Coverity (CID 1358496) warns that the cleanup code doesn't unlock the
mutex (which is arguably kind of stupid, since the only case that can
happen is when mtx_unlock() failed!). But, mtx_unlock() isn't going to
fail -- the mutex was locked by this thread just a few lines above it.
diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index d8448f4..65a3a62 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -2585,10 +2585,7 @@
 
          ret = cnd_wait(&dri2_sync->cond, &dri2_sync->mutex);
 
-         if (mtx_unlock(&dri2_sync->mutex)) {
-            ret = EGL_FALSE;
-            goto cleanup;
-         }
+         mtx_unlock(&dri2_sync->mutex);
 
          if (ret) {
             _eglError(EGL_BAD_PARAMETER, "eglClientWaitSyncKHR");
@@ -2619,10 +2616,7 @@
 
             ret = cnd_timedwait(&dri2_sync->cond, &dri2_sync->mutex, &expire);
 
-            if (mtx_unlock(&dri2_sync->mutex)) {
-               ret = EGL_FALSE;
-               goto cleanup;
-            }
+            mtx_unlock(&dri2_sync->mutex);
 
             if (ret)
                if (ret == thrd_busy) {