hyperv: hyperv_fb: match wait_for_completion_timeout return type

The return type of wait_for_completion_timeout is unsigned long not
int. This patch fixes up the declarations only.

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>