serial: 8250: 8250_omap: Move locking out from __dma_rx_do_complete()

Caller functions of __dma_rx_do_complete() already hold rx_dma_lock.
Therefore move locking out of the function to avoid need to release and
reacquire lock.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200319110344.21348-4-vigneshr@ti.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>