msm: dma: don't read from FLUSH2 register

The FLUSH2 register contains only reserved bits, and software is not
supposed to access it at all. Reading it on 9x15 causes external faults,
so remove this access.

Change-Id: I65b08b92d20a4f0dcfad9cabe9013f364dfc92f3
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>