UIO base driver should only free_irq that it has requested.
UIO supports drivers without interrupts (irq == 0) or custom handlers.

This fixes warnings like:

WARNING: CPU: 1 PID: 5478 at kernel/irq/manage.c:1244 __free_irq+0xa9/0x1e0()
Trying to free already-free IRQ 0
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>