linux-user: Sink call to do_safe_futex

Leave only the argument adjustments within the shift,
and sink the actual syscall to the end.  Sink the
timespec conversion as well, as there will be more users.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220829021006.67305-3-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>