ext4: Do not override ext2 or ext3 if built they are built as modules

The CONFIG_EXT4_USE_FOR_EXT23 option must not try to take over the
ext2 or ext3 file systems if the those file system drivers are
configured to be built as mdoules.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/ext4/Kconfig
Simple merge

diff --cc fs/ext4/super.c
Simple merge