target/sh4: Update DisasContextBase.insn_start

Match the extra inserts of INDEX_op_insn_start, fixing
the db->num_insns != 1 assert in translator_loop.

Fixes: dcd092a0636 ("accel/tcg: Improve can_do_io management")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
1 file changed