[nrf528xx] add volatile mark to nrf uart read/write buffers (#4652)
[nrf528xx] add volatile mark to nrf uart read/write buffers (#4652)

These buffers are touched in volatile and should be marked as volatile.
chshu/openthread,bukepo/openthread,jwhui/openthread,jwhui/openthread,chshu/openthread,lanyuwen/openthread,lanyuwen/openthread,chshu/openthread,librasungirl/openthread,openthread/openthread,chshu/openthread,chshu/openthread,lanyuwen/openthread,bukepo/openthread,openthread/openthread,lanyuwen/openthread,bukepo/openthread,srickardti/openthread,abtink/openthread,librasungirl/openthread,srickardti/openthread,jwhui/openthread,srickardti/openthread,lanyuwen/openthread,openthread/openthread,librasungirl/openthread,chshu/openthread,abtink/openthread,openthread/openthread,lanyuwen/openthread,abtink/openthread,srickardti/openthread,librasungirl/openthread,abtink/openthread,jwhui/openthread,bukepo/openthread