msm_rtb: Evaluate parameter only once in reads/writes

This reverts commit fc44c0ba ("msm_rtb: Don't lose
the __user tag on relaxed reads/writes"). This causes
address parameter, with side effects, to be evaluated
more than once.

Change-Id: Ib37665763736bdf562afcc8335b014a2724a7598
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>