docs: perf: Fix PMU instance name of hisi-pcie-pmu

[ Upstream commit eb79f12b ]

The PMU instance will be called hisi_pcie<sicl>_core<core> rather than
hisi_pcie<sicl>_<core>. Fix this in the documentation.

Fixes: c8602008

 ("docs: perf: Add description for HiSilicon PCIe PMU driver")
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20221117084136.53572-3-yangyicong@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>