R600: Unbreak GCC build.

operator++ on an enum is not legal. clang happens to accept it anyways, I think
that's a known bug.

llvm-svn: 185269

llvm/lib/Target/R600/R600InstrInfo.cpp

@@ -398,7 +398,8 @@ NextPossibleSolution(
   }
   if (ResetIdx == -1)
     return false;
-  SwzCandidate[ResetIdx]++;
+  int NextSwizzle = SwzCandidate[ResetIdx] + 1;
+  SwzCandidate[ResetIdx] = (R600InstrInfo::BankSwizzle)NextSwizzle;
   return true;
 }