drm/dp-mst-helper: Avoid reading uninitialized value

A static analysis tool tells me that we could try to read an
uninitialized 'ret' value. Plug that.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
1 file changed