firewire: ohci: Check LPS before register access on pci removal

A pci device can be removed while in its suspended state. If the ohci
host controller is suspended, the PHY is also in low-power mode and
LPS is disabled. If LPS is disabled, most of the host registers aren't
accessible, including IntMaskClear. Furthermore, access to these registers
when LPS is disabled can cause hard lockups on some hardware. Since
interrupts are already disabled in this mode, further action is
unnecessary.

Test LPS before attempting to write IntMaskClear to disable interrupts.

[Stefan R: whitespace changes]

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>