3c503: fix broken IRQ autoprobing

Fix broken IRQ autoprobing in 3c503 driver:
 - improper IRQ freeing (does not free IRQs causes WARN)
 - missing break when an working IRQ is found

The driver works with this patch.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Reviewed-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>