arm64: perf: Remove redundant initialization in perf_event.c

The initialization of value in function armv8pmu_read_hw_counter()
and armv8pmu_read_counter() seem redundant, as they are soon updated.
So, We can remove them.

Signed-off-by: Qi Liu <liuqi115@huawei.com>
Link: https://lore.kernel.org/r/1617275801-1980-1-git-send-email-liuqi115@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>