Fix falling back to system mount command will fail when callin ensure_path_mounted(filename)

If filename is not the mount point, this will miserably fail to mount
exp: Bug will be revealed when using fstype2=auto for external_sd and trying to ensure_path_mounted("/external_sd/path/to/filename")
This fix also takes into account when checking sdcard marker in edifyscripting.c to ensure mount /emmc to /sdcard if needed