ltp: Fix races in mmap1

Make map_address a volatile pointer so that it is dereferenced in
read_mem() after read_lock is set.

Also read_lock must protect the verbose printf that reads from map_address
as well.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>