tcg: Work around clang bug wrt enum ranges, part 2

A previous patch patch changed the type of REG from int
to enum TCGReg, which provokes the following bug in clang:

  https://llvm.org/bugs/show_bug.cgi?id=16154

Signed-off-by: Richard Henderson  <rth@twiddle.net>

tcg/tcg.c

@@ -1602,7 +1602,7 @@ static void dump_regs(TCGContext *s)
 
 static void check_regs(TCGContext *s)
 {
-    TCGReg reg;
+    int reg;
     int k;
     TCGTemp *ts;
     char buf[64];