glamor: Don't try to free the pixmap priv if we fail to allocate FBO.

Fixes a regression since a2a2f6e34b.  I
missed this in testing on x86, because we never fail to allocate an
FBO.  We do hit this path on VC4, though.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit ea03e314f9)

glamor/glamor.c

@@ -207,7 +207,6 @@ glamor_create_pixmap(ScreenPtr screen, int w, int h, int depth,
 
     if (fbo == NULL) {
         fbDestroyPixmap(pixmap);
-        free(pixmap_priv);
         return fbCreatePixmap(screen, w, h, depth, usage);
     }