We don't actually need the result of the read, only to probe that the
memory mapping exists.  This is exactly what probe_access does.

This is also the only user of any cpu_ld*_code_ra function.
Removing this allows the interface to be removed shortly.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>