[PATCH] spi: dw: fix build error by selecting MULTIPLEXER

[Randy Dunlap <rdunlap@xxxxxxxxxxxxx>]

Fix build error for spi-dw-bt1.o by selecting MULTIPLEXER.

hppa-linux-ld: drivers/spi/spi-dw-bt1.o: in function `dw_spi_bt1_sys_init':
(.text+0x1ac): undefined reference to `devm_mux_control_get'

Fixes: abf00907538e ("spi: dw: Add Baikal-T1 SPI Controller glue driver")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
Cc: Ramil Zaripov <Ramil.Zaripov@xxxxxxxxxxxxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: linux-spi@xxxxxxxxxxxxxxx
---
 drivers/spi/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20201113.orig/drivers/spi/Kconfig
+++ linux-next-20201113/drivers/spi/Kconfig
@@ -255,6 +255,7 @@ config SPI_DW_MMIO
 config SPI_DW_BT1
 	tristate "Baikal-T1 SPI driver for DW SPI core"
 	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
+	select MULTIPLEXER
 	help
 	  Baikal-T1 SoC is equipped with three DW APB SSI-based MMIO SPI
 	  controllers. Two of them are pretty much normal: with IRQ, DMA,