Add a dummy return to fix a Watcom warning.

git-svn-id: svn://svn.cc65.org/cc65/trunk@3980 b7a2c559-68d2-44c3-8de9-860c34a00d81

src/common/cpu.c

@@ -110,6 +110,8 @@ int ValidAddrSizeForCPU (unsigned char AddrSize)
 
         default:
             FAIL ("Invalid address size");
+            /* NOTREACHED */
+            return 0;
     }
 }