serial: msm_geni_serial: Bailout from wait_for_transfers_inflight

This change is to avoid potential race btw stop rx and incoming
SOC RX data in parallel. During suspend path wait_for_transfers_inflight()
logic will check for TX/RX data pending for completion. Check for RX_LEN_IN
status in wait_for_transfers_inflight() and return -EBUSY to avoid race
between stop_rx and SOC RX data.

Change-Id: I28702d3dc11ee4b6d3fe5b4bad9a19099d8cf725
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>