p54usb: fix off-by-one on !CONFIG_PM

The ISL3887 chip needs a USB reset, whenever the
usb-frontend module "p54usb" is reloaded.

This patch fixes an off-by-one bug, if the user
is running a kernel without the CONFIG_PM option
set and for some reason (e.g.: compat-wireless)
wants to switch between different p54usb modules.

Cc: <stable@kernel.org>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>