docs: perf: Address some html build warnings

Fix following html build warnings:
Documentation/admin-guide/perf/hisi-pmu.rst:61: WARNING: Unexpected indentation.
Documentation/admin-guide/perf/hisi-pmu.rst:62: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/admin-guide/perf/hisi-pmu.rst:69: WARNING: Unexpected indentation.
Documentation/admin-guide/perf/hisi-pmu.rst:70: WARNING: Block quote ends without a blank line; unexpected unindent.
Documentation/admin-guide/perf/hisi-pmu.rst:83: WARNING: Unexpected indentation.

Fixes: 9b86b1b4 ("docs: perf: Add new description on HiSilicon uncore PMU v2")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Qi Liu <liuqi115@huawei.com>
Link: https://lore.kernel.org/r/1617021121-31450-1-git-send-email-liuqi115@huawei.com


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