The ->close, ->suspend and ->resume hooks assume presence of a valid IRQ
if the device is wakeup capable. However it's entirely possible that
wakeup was enabled by some other entity besides this driver and in this
case the user will get a WARN splat if no valid IRQ was found. Avoid by
checking if the IRQ is valid, i.e. > 0.
Case in point: On recent MacBook Pros, the Bluetooth device lacks an
IRQ (because host wakeup is handled by the SMC, independently of the
operating system), but it does possess a _PRW method (which specifies
the SMC's GPE as wake event). The ACPI core therefore automatically
marks the physical Bluetooth device wakeup capable upon binding it to
its ACPI companion: