Add fall through comment for Coverity.
# gpg: Signature made Wed 08 Apr 2020 16:28:12 BST
# gpg: using RSA key
7A481E78868B4DB6A85A05C064DF38E8AF7E215F
# gpg: issuer "richard.henderson@linaro.org"
# gpg: Good signature from "Richard Henderson <richard.henderson@linaro.org>" [full]
# Primary key fingerprint: 7A48 1E78 868B 4DB6 A85A 05C0 64DF 38E8 AF7E 215F
* remotes/rth/tags/pull-rx-
20200408:
target/rx/translate: Add missing fall through comment
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>