spi_qsd: Fix bug in multi-xfer bam mode transaction

Spi doesn't handle multiple xfer per message scenario
(eg:Rd->Wr or Wr->Rd) correctly and spi request
stuck indefinetly in while loop when total byte count
is not 0.

increment both(rx,tx) references so next bam
transaction will be queued correctly. Flush the
bam pipes after each transactions.

CRs-Fixed: 637693
Change-Id: I455df38be2f9687b1eb2a704466f6974dfb83a22
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>