mtd: dc21285: use raw spinlock functions for nw_gpio_lock

mtd: dc21285: use raw spinlock functions for nw_gpio_lock

Since commit bd31b85960a7 (which is in 3.2-rc1) nw_gpio_lock is a raw spinlock
that needs usage of the corresponding raw functions.

This fixes:

  drivers/mtd/maps/dc21285.c: In function 'nw_en_write':
  drivers/mtd/maps/dc21285.c:41:340: warning: passing argument 1 of 'spinlock_check' from incompatible pointer type
    spin_lock_irqsave(&nw_gpio_lock, flags);

  In file included from include/linux/seqlock.h:35:0,
                   from include/linux/time.h:5,
                   from include/linux/stat.h:18,
                   from include/linux/module.h:10,
                   from drivers/mtd/maps/dc21285.c:8:
  include/linux/spinlock.h:299:102: note: expected 'struct spinlock_t *' but argument is of type 'struct raw_spinlock_t *'
   static inline raw_spinlock_t *spinlock_check(spinlock_t *lock)
                                                                                                        ^
  drivers/mtd/maps/dc21285.c:43:25: warning: passing argument 1 of 'spin_unlock_irqrestore' from incompatible pointer type
    spin_unlock_irqrestore(&nw_gpio_lock, flags);
                           ^
  In file included from include/linux/seqlock.h:35:0,
                   from include/linux/time.h:5,
                   from include/linux/stat.h:18,
                   from include/linux/module.h:10,
                   from drivers/mtd/maps/dc21285.c:8:
  include/linux/spinlock.h:370:91: note: expected 'struct spinlock_t *' but argument is of type 'struct raw_spinlock_t *'
   static inline void spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)

Fixes: bd31b85960a7 ("locking, ARM: Annotate low level hw locks as raw")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>