[ARM] msm: smd: Update the correct fTAIL pointer after reading from fifo

When we read data out of the sender's fifo, we need to advance the sender's
tail pointer, not the receiver's.

Signed-off-by: Haley Teng <Haley_Teng@htc.com>
Acked-by: Dima Zavin <dima@android.com>
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>