pinctrl: nomadik: shut up a warning for flags

The irq flags variable gets a warning like this after
commit bf4dae5c
"pinctrl: nomadik: delete ancient pin control API":

In file included from include/linux/seqlock.h:29:0,
                 from include/linux/time.h:5,
                 from include/linux/stat.h:18,
                 from include/linux/module.h:10,
                 from
drivers/pinctrl/pinctrl-nomadik.c:14:
drivers/pinctrl/pinctrl-nomadik.c: In function 'nmk_pmx_enable':
include/linux/spinlock.h:348:122: warning:
'flags' may be used uninitialized in this function
[-Wmaybe-uninitialized]
  raw_spin_unlock_irqrestore(&lock->rlock, flags);
                                                   ^
drivers/pinctrl/pinctrl-nomadik.c:1515:16: note:
'flags' was declared here
  unsigned long flags;

The function is question was never changed but it appears
the semantic checker could previously determine that the code
path that would use the flags was going to either use it or
not, but now it can't for some reason. Just fix it up.

Reported-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>