p54pci: add handling of signal case

if(!wait_for_completion_interruptible_timeout(...))
only handles the timeout case - this patch adds handling the
signal case the same as timeout.

Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
Acked-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>