perf: llcc: Remove all unused local variables from llcc pmu driver

Compilation of LLCC PMU driver with Clang is warning of many unused
local variables. Remove these for a cleaner compilation.

Change-Id: I8f99faba87cb5de141b8509c2dde11db24a357cf
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>