tcg/arm: Fix SIGILL in tcg_out_qemu_st_direct

tcg/arm: Fix SIGILL in tcg_out_qemu_st_direct

When tcg_out_qemu_st_{index,direct} were merged, the direct case for
MO_64 was omitted, causing qemu_st_i64 to be encoded as 0xffffffff due
to underflow when adding h.base and h.index.

Fixes: 1df6d611bdc2 ("tcg/arm: Introduce HostAddress")
Signed-off-by: Joseph Burt <caseorum@gmail.com>
Message-Id: <20240121211439.100829-1-caseorum@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>