fstab.common: Fix mmc sdcard path for 6.x and newer kernel versions am: f988e76cb7

Original change: https://android-review.googlesource.com/c/device/linaro/dragonboard/+/2868694

Change-Id: Id5f350aa86ff7a5aa97554521ae9e882e351b467
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>