mediatek: drop leading + from config

Signed-off-by: John Crispin <[email protected]>

target/linux/mediatek/mt7629/config-4.19

@@ -235,7 +235,7 @@ CONFIG_MTD_NAND=y
 CONFIG_MTD_NAND_CORE=y
 CONFIG_MTD_NAND_ECC=y
 CONFIG_MTD_NAND_MTK=y
-+CONFIG_MTD_SPI_NAND=y
+CONFIG_MTD_SPI_NAND=y
 CONFIG_MTD_SPI_NOR=y
 CONFIG_MTD_SPLIT_FIRMWARE=y
 CONFIG_MTD_SPLIT_FIT_FW=y