Revert "serial: omap: unlock the port lock"

This reverts commit 0324a821.

That commit tried to fix a deadlock problem when using
hci_ldisc, but it turns out the bug was in hci_ldsic
all along where it was calling ->write() from within
->write_wakeup() callback.

The problem is that ->write_wakeup() was called with
port lock held and ->write() tried to grab the same
port lock.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>