1. rpmsgdev ioctl: should assgin back the client return value to
cookie->result, then this return value can be returned to the
application;
2. rpmsgdev seek: the type "off_t" may be 64bit, so modify the offset
in "struct rpmsgdev_lseek" to int64_t too;
3. rpmsgdev_seek: the rpmsgdev_seek in client should update the
filep->f_pos after the seek operation;
Signed-off-by: wangbowen6 <wangbowen6@xiaomi.com>
84fa994f51