ssb: add gpio_to_irq

The old bcm47xx gpio code had support for gpio_to_irq, but the new
code did not provide this function, but returned -ENXIO all the time.
This patch adds the missing function.

arch/mips/bcm47xx/wgt634u.c calls gpio_to_irq() and got the correct irq
number with the old gpio handling code. With this patch the code in
wgt634u.c should work again. I do not have a wgt634u to test this.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/linux/ssb/ssb_driver_mips.h b/include/linux/ssb/ssb_driver_mips.h
index 07a9c7a..afe79d4 100644
--- a/include/linux/ssb/ssb_driver_mips.h
+++ b/include/linux/ssb/ssb_driver_mips.h
@@ -45,6 +45,11 @@
 {
 }
 
+static inline unsigned int ssb_mips_irq(struct ssb_device *dev)
+{
+	return 0;
+}
+
 #endif /* CONFIG_SSB_DRIVER_MIPS */
 
 #endif /* LINUX_SSB_MIPSCORE_H_ */