There is a plan to build the kernel with -Wimplicit-fallthrough and
these places in the code produced warnings (W=1). Fix them up.
This commit remove the following warnings:
fs/ext4/hash.c:233:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
fs/ext4/hash.c:246:15: warning: this statement may fall through [-Wimplicit-fallthrough=]