randconfig got a problem with ucb1400_core.c (config attached)

drivers/built-in.o:(.data+0x15ab4): undefined reference to `ac97_bus_type'
make: *** [.tmp_vmlinux1] Error 1

ucb1400 is an ac97 audio codec. express this dependency in Kconfig

Signed-off-by: Sergio Luis <sergio@larces.uece.br>
Cc: Marek Vasut <marek.vasut@gmail.com>

drivers/mfd/Kconfig |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 0dae245..fa851c5 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -52,6 +52,7 @@ config HTC_PASIC3
 
 config UCB1400_CORE
 	tristate "Philips UCB1400 Core driver"
+	select AC97_BUS
 	help
 	  This enables support for the Philips UCB1400 core functions.
 	  The UCB1400 is an AC97 audio codec.