drivers/rtc/rtc-da9052.c: remove redundant private structure field

Remove redundant irq field in private rtc structure.

Signed-off-by: Anthony Olech <anthony.olech.opensource@diasemi.com>
Acked-by: David Dajun Chen <david.chen@diasemi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>