ASoC: wm8994: Add depends on MFD core

ASoC: wm8994: Add depends on MFD core

The ASoC driver should not be used without the MFD component. This was
causing randconfig issues with regmap IRQ which is selected by the MFD
part of the wm8994 driver.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501061337.R0DlBUoD-lkp@intel.com/
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20250106154639.3999553-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>