n_tty: Get read_cnt through accessor
n_tty: Get read_cnt through accessor

Prepare for replacing read_cnt field with computed value.

Signed-off-by: Peter Hurley <4b8373d016f277527198385ba72fda0feb5da015@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs