[PATCH v3] staging: wfx: fix an undefined reference error when CONFIG_MMC=m

[zhong jiang]

I hit the following error when compile the kernel.

drivers/staging/wfx/main.o: In function `wfx_core_init':
/home/z00352263/linux-next/linux-next/drivers/staging/wfx/main.c:488: undefined reference to `sdio_register_driver'
drivers/staging/wfx/main.o: In function `wfx_core_exit':
/home/z00352263/linux-next/linux-next/drivers/staging/wfx/main.c:496: undefined reference to `sdio_unregister_driver'
drivers/staging/wfx/main.o:(.debug_addr+0x1a8): undefined reference to `sdio_register_driver'
drivers/staging/wfx/main.o:(.debug_addr+0x6f0): undefined reference to `sdio_unregister_driver'

Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
---
v2->v3:
    We'd better not use #ifdef in .c file to use IS_ENABLED instead.

v1->v2:
    We should prefer to current dependencies rather than force to enable. 

 drivers/staging/wfx/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/wfx/Makefile b/drivers/staging/wfx/Makefile
index 0d9c1ed..77d68b7 100644
--- a/drivers/staging/wfx/Makefile
+++ b/drivers/staging/wfx/Makefile
@@ -19,6 +19,6 @@ wfx-y := \
 	sta.o \
 	debug.o
 wfx-$(CONFIG_SPI) += bus_spi.o
-wfx-$(subst m,y,$(CONFIG_MMC)) += bus_sdio.o
+wfx-$(CONFIG_MMC) += bus_sdio.o
 
 obj-$(CONFIG_WFX) += wfx.o
-- 
1.7.12.4