Fix sdcard's FUSE_FSYNCDIR handling.

For a file the FUSE fh is a struct handle containing an int fd;
for a directory it's a struct dirhandle containing a DIR*. Fix
handle_fsync to extract the file descriptor appropriately in
both cases.

Bug: 14613980
Change-Id: I45515cff6638e27a99b849e6fc639d355dbb4d27