fatfs: add support for mmc disks when generating FF_VOLUME_STRS

add zephyr,mmc-disk's disk names as they were missing causing fatfs to
be unusable on boards that had otherwise valid DT configuration for
the mmc disks.

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

modules/fatfs/zephyr_fatfs_config.h

@@ -113,6 +113,7 @@
 	DT_FOREACH_STATUS_OKAY(zephyr_flash_disk, _FF_DISK_NAME) \
 	DT_FOREACH_STATUS_OKAY(zephyr_ram_disk, _FF_DISK_NAME) \
 	DT_FOREACH_STATUS_OKAY(zephyr_sdmmc_disk, _FF_DISK_NAME) \
+	DT_FOREACH_STATUS_OKAY(zephyr_mmc_disk, _FF_DISK_NAME) \
 	DT_FOREACH_STATUS_OKAY(st_stm32_sdmmc, _FF_DISK_NAME)
 
 #undef FF_VOLUMES