msm: gpio-v2: Fix lockdep warning

In similar fashion as b5eee2fd (ARM: mxc: Add missing lockdep
annotation, 2011-04-04) add a lock class so that lockdep knows
the gpio irqs are always locked correctly with respect to the
descriptor lock class.

=============================================
[ INFO: possible recursive locking detected ]
3.0.21-g51ce160-00020-g8eb5789-dirty #2894
---------------------------------------------
swapper/1 is trying to acquire lock:
 (&irq_desc_lock_class){-.....}, at: [<c01ceaf0>] __irq_get_desc_lock+0x74/0x8c

but task is already holding lock:
 (&irq_desc_lock_class){-.....}, at: [<c01ceaf0>] __irq_get_desc_lock+0x74/0x8c

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&irq_desc_lock_class);
  lock(&irq_desc_lock_class);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by swapper/1:
 #0:  (&__lockdep_no_validate__){+.+.+.}, at: device_attach+0x18/0xa4
 #1:  (&__lockdep_no_validate__){+.+.+.}, at: device_attach+0x18/0xa4
 #2:  (&irq_desc_lock_class){-.....}, at: __irq_get_desc_lock+0x74/0x8c

Change-Id: Icc0058370de4db17ae4fadb66f5fe970c37ecc6c
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>