ext4: fix Kconfig documentation for CONFIG_EXT4_DEBUG

Fox the Kconfig documentation for CONFIG_EXT4_DEBUG to match the
change made by commit a0b30c12: ext4: use module parameters instead
of debugfs for mballoc_debug
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

fs/ext4/Kconfig

@@ -71,4 +71,5 @@ config EXT4_DEBUG
 	  Enables run-time debugging support for the ext4 filesystem.
 
 	  If you select Y here, then you will be able to turn on debugging
-	  with a command such as "echo 1 > /sys/kernel/debug/ext4/mballoc-debug"
+	  with a command such as:
+		echo 1 > /sys/module/ext4/parameters/mballoc_debug