ANDROID: fs/fuse: Backing move returns EXDEV if TO not backed

In a move operation, if the FROM file has a backing inode associated and
is handled in backing, it might happen that the TO file does not have a
backing path associated (yet), maybe because the FUSE daemon didn't have
the chance to traverse it.
Thus this special case would mistakenly trigger EBADF, while EXDEV is
more appropriate.

Bug: 202785178
Test: mv /storage/emulated/0/Android/data/<pkg>/file /sdcard/DCIM
Signed-off-by: Alessio Balsini <balsini@google.com>
Change-Id: I513c0e17c128ed9181a6b96fbf9f0b950e78be77