Add typecast to silence -Wswitch warning introduced by r153153.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153155 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp

@@ -99,7 +99,7 @@ public:
     // Used to point to big endian bytes
     unsigned FullSize;
 
-    switch (Kind) {
+    switch ((unsigned)Kind) {
     case Mips::fixup_Mips_16:
       FullSize = 2;
       break;