common-user: Fix tail calls to safe_syscall_set_errno_tail

common-user: Fix tail calls to safe_syscall_set_errno_tail

For the ABIs in which the syscall return register is not
also the first function argument register, move the errno
value into the correct place.

Fixes: a3310c0397e2 ("linux-user: Move syscall error detection into safe_syscall_base")
Reported-by: Laurent Vivier <laurent@vivier.eu>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220104190454.542225-1-richard.henderson@linaro.org>