ext4: Fix Kconfig typo for ext4dev

Looks like there is one more instance where ext4dev should be changed
to ext4 because the module name will be "ext4" unless EXT4DEV_COMPAT
is selected.

Signed-off-by: Manish Katiyar <mkatiyar@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/Kconfig

@@ -160,7 +160,7 @@ config EXT4_FS
 	  filesystem initially.
 
 	  To compile this file system support as a module, choose M here. The
-	  module will be called ext4dev.
+	  module will be called ext4.
 
 	  If unsure, say N.