rtc-ds1553: drop IRQF_SHARED

IRQF_SHARED should not be used with IRQF_DISABLED.  There is no in-tree
user of this driver and only out-of-tree user I know uses a dedicated irq
line for this RTC.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>