package/rtl8723ds: fix build failure due to missing Linux CONFIG_MMC

This Wi-Fi module has an SDIO interface so we need to make sure Linux
has CONFIG_MMC (that include SDIO APIs) enabled.

Fixes:

  http://autobuild.buildroot.net/results/1bb71019b7edd7f195223a85c81f70e5a60518f0/

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 80323a534b12803fa25d55e3c5e2c8a527ca5863)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/rtl8723ds/rtl8723ds.mk

@@ -17,6 +17,7 @@ define RTL8723DS_LINUX_CONFIG_FIXUPS
 	$(call KCONFIG_ENABLE_OPT,CONFIG_NET)
 	$(call KCONFIG_ENABLE_OPT,CONFIG_WIRELESS)
 	$(call KCONFIG_ENABLE_OPT,CONFIG_CFG80211)
+	$(call KCONFIG_ENABLE_OPT,CONFIG_MMC)
 endef
 
 $(eval $(kernel-module))