ARM: 6311/2: mmci: work with only one irq

The DBx500 variants have only one IRQ line hooked up.  Allow these (and
any other implementations which choose to use only one irq) to work by
directing the PIO interrupts also to the first IRQ line.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>