[ARM] rtc-sa1100: fix compiler warnings and error cleanup

Fix:
drivers/rtc/rtc-sa1100.c: In function `sa1100_rtc_proc':
drivers/rtc/rtc-sa1100.c:298: warning: unsigned int format, long unsigned int arg (arg 3)

and arrange for sa1100_rtc_open() to pass the devid to free_irq()
rather than NULL.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>