mfd: wm8994: Silence bogus warning in wm8994_device_init()

'patch_regs' cannot be used uninitialized in wm8994_device_init(),
because 'patch_regs' was already guarded by 'regmap_patch'.
Thus, that's a bogus warning.

Without this patch, the build warning happens as below:

drivers/mfd/wm8994-core.c: In function 'wm8994_i2c_probe':
drivers/mfd/wm8994-core.c:595:7: warning: 'patch_regs' may be used uninitialized in this function [-Wuninitialized]
drivers/mfd/wm8994-core.c:408:14: note: 'patch_regs' was declared here

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>