Remove the unreachable code detected by clang.

  $ make HOSTCC=clang HOSTCFLAGS=-Wunreachable-code defconfig
    [ snip ]
  scripts/kconfig/expr.c:1134:2: warning: code will never be executed [-Wunreachable-code]
          printf("[%dgt%d?]", t1, t2);
          ^~~~~~
  1 warning generated.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>