MIPS: Fix fall-through warnings for Clang

Fix the following fallthrough warnings:

arch/mips/mm/tlbex.c:1386:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
arch/mips/mm/tlbex.c:2173:3: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/60edca25.k00ut905IFBjPyt5%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
1 file changed