linux-user: Fix shmat() strace

linux-user: Fix shmat() strace

The indices of arguments passed to print_shmat() are all off-by-1,
because arg1 is the ipc() command. Fix them.

New output for linux-shmat-maps test:

    3501769 shmat(4784214,0x0000000000800000,SHM_RND) = 0

Fixes: 9f7c97324c27 ("linux-user: Add strace for shmat")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240325192436.561154-3-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>