pty: Don't claim slave's ctrl_lock for master's packet mode

pty: Don't claim slave's ctrl_lock for master's packet mode

The slave's ctrl_lock serializes updates to the ctrl_status field
only, whereas the master's ctrl_lock serializes updates to the
packet mode enable (ie., the master does not have ctrl_status and
the slave does not have packet mode). Thus, claiming the slave's
ctrl_lock to access ->packet is useless.

Unlocked reads of ->packet are already smp-safe.

Signed-off-by: Peter Hurley <[email protected]>
Reviewed-by: Alan Cox <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>