msm: ipa3: Use read memory barrier before reading events

Use read memory barrier before reading event from event ring.
Since ring is shared resource between IPA h/w and IPA driver
dma_rmb is used to ensure memory write is complete before
reading from driver.

Change-Id: If2b86ee1acecbdfc75beb327eb60f876e6915d8f
Signed-off-by: Ashok Vuyyuru <avuyyuru@codeaurora.org>