ARM: imx: MACH_MX31ADS_WM1133_EV1 needs REGULATOR_WM8350

MACH_MX31ADS_WM1133_EV1 already depends on REGULATOR_WM8350,
but that still allows REGULATOR_WM8350 to be a loadable
module. Depending on REGULATOR_WM8350 to be built-in
ensures we cannot create a broken configuration.

Without this patch, building allmodconfig results in:

arch/arm/mach-imx/built-in.o: In function `mx31_wm8350_init':
arch/arm/mach-imx/mach-mx31ads.c:461: undefined reference to `wm8350_register_regulator'
arch/arm/mach-imx/mach-mx31ads.c:471: undefined reference to `wm8350_dcdc_set_slot'
arch/arm/mach-imx/mach-mx31ads.c:473: undefined reference to `wm8350_isink_set_flash'
arch/arm/mach-imx/mach-mx31ads.c:480: undefined reference to `wm8350_dcdc25_set_mode'
arch/arm/mach-imx/mach-mx31ads.c:485: undefined reference to `wm8350_register_led'

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Axel Lin <axel.lin@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>