rtc: lockdep fix/workaround

rtc: lockdep fix/workaround

BUG: warning at kernel/lockdep.c:1816/trace_hardirqs_on() (Not tainted)
 [<c04051ee>] show_trace_log_lvl+0x58/0x171
 [<c0405802>] show_trace+0xd/0x10
 [<c040591b>] dump_stack+0x19/0x1b
 [<c043abee>] trace_hardirqs_on+0xa2/0x11e
 [<c06143c3>] _spin_unlock_irq+0x22/0x26
 [<c0541540>] rtc_get_rtc_time+0x32/0x176
 [<c0419ba4>] hpet_rtc_interrupt+0x92/0x14d
 [<c0450f94>] handle_IRQ_event+0x20/0x4d
 [<c0451055>] __do_IRQ+0x94/0xef
 [<c040678d>] do_IRQ+0x9e/0xbd
 [<c0404a49>] common_interrupt+0x25/0x2c
DWARF2 unwinder stuck at common_interrupt+0x25/0x2c

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Adrian Bunk <bunk@stusta.de>