msm: bam_dmux: extend tx list lock around sps_transfer_one()

The tx list must be kept in sync with the packets queued to BAM via
sps_transfer_one().  Releasing the tx list lock allows a small window
to exist where the tx list could lose sync and possibly cause a crash
later on.  Since sps_transfer_one() can be run in atomic context, do
not release the list lock until after sps_transfer_one() returns.

Change-Id: Ibd79e983c04a1e050ec83252d0156844f6af3594
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>