drivers/rtc/rtc-sirfsoc.c: fix kernel warning during wakeup

drivers/rtc/rtc-sirfsoc.c: fix kernel warning during wakeup

enable_irq_wake() might fail, if so, we will see kernel warning in resume
entries due to it always calls disable_irq_wake().

  WARNING: at kernel/irq/manage.c:529 irq_set_irq_wake+0xc4/0xf0()
  Unbalanced IRQ 52 wake disable
  Modules linked in: ipv6 libcomposite configfs
  CPU: 0 PID: 1591 Comm: ash Tainted: G        W    3.10.0-00854-gdbd86d4-dirty #100
    (unwind_backtrace+0x0/0xf8) from (show_stack+0x10/0x14)
    (show_stack+0x10/0x14) from (warn_slowpath_common+0x54/0x68)
    (warn_slowpath_common+0x54/0x68) from (warn_slowpath_fmt+0x30/0x40)
    (warn_slowpath_fmt+0x30/0x40) from (irq_set_irq_wake+0xc4/0xf0)
    (irq_set_irq_wake+0xc4/0xf0) from (sirfsoc_rtc_restore+0x30/0x38)
    (sirfsoc_rtc_restore+0x30/0x38) from (platform_pm_restore+0x2c/0x50)
    (platform_pm_restore+0x2c/0x50) from (dpm_run_callback.clone.6+0x30/0xb0)
    (dpm_run_callback.clone.6+0x30/0xb0) from (device_resume+0x88/0x134)
    (device_resume+0x88/0x134) from (dpm_resume+0x114/0x230)
    (dpm_resume+0x114/0x230) from (hibernation_snapshot+0x178/0x1d0)
    (hibernation_snapshot+0x178/0x1d0) from (hibernate+0x130/0x1dc)
    (hibernate+0x130/0x1dc) from (state_store+0xb4/0xc0)
    (state_store+0xb4/0xc0) from (kobj_attr_store+0x14/0x20)
    (kobj_attr_store+0x14/0x20) from (sysfs_write_file+0xfc/0x17c)
    (sysfs_write_file+0xfc/0x17c) from (vfs_write+0xc8/0x194)
    (vfs_write+0xc8/0x194) from (SyS_write+0x40/0x6c)
    (SyS_write+0x40/0x6c) from (ret_fast_syscall+0x0/0x30)

To avoid unbalanced "IRQ wake disable", ensure that disable_irq_wake() is
called only when enable_irq_wake() have been successfully enabled.

Signed-off-by: Xianglong Du <Xianglong.Du@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>