Fix a warning in the EGL winsys
Fix a warning in the EGL winsys

_cogl_egl_query_wayland_buffer was using _COGL_RETURN_IF_FAIL but the
function needs to return a CoglBool so it was giving a warning.

gcampax/cogl,djdeath/cogl,gcampax/cogl,gcampax/cogl,gcampax/cogl,djdeath/cogl,djdeath/cogl