mx31pdk: Fix pmic_init() argument

On mx31pdk board the PMIC is connected via SPI interface, so it does not make
sense to pass I2C_PMIC into the pmic_init() interface.

Pass the SPI bus number via CONFIG_FSL_PMIC_BUS option instead.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/board/freescale/mx31pdk/mx31pdk.c b/board/freescale/mx31pdk/mx31pdk.c
index 148b4f4..13b9d51 100644
--- a/board/freescale/mx31pdk/mx31pdk.c
+++ b/board/freescale/mx31pdk/mx31pdk.c
@@ -85,7 +85,7 @@
 	struct pmic *p;
 	int ret;
 
-	ret = pmic_init(I2C_PMIC);
+	ret = pmic_init(CONFIG_FSL_PMIC_BUS);
 	if (ret)
 		return ret;