msm: sps: add verification of IOVECs for sps_transfer

1> Check if the content of input IOVECs are valid.
2> The flag checking has existed in sps_transfer_one(). Move
this part to a separate function since it is common in both
sps_transfer_one() and sps_transfer().

Change-Id: I3835b60e216600496192ea0e84440d420f10adec
Signed-off-by: Yan He <yanhe@codeaurora.org>