cpupower: fix reference to nonexistent document

stable inclusion
from stable-v6.6.2
commit da4f8ab224dc7ed64211b102b5c9cef541385711
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8IW7G

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=da4f8ab224dc7ed64211b102b5c9cef541385711



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[ Upstream commit 6feb1a9641197ee630bf43b5c34ea1d9f8b4a0aa ]

This file was renamed from .txt to .rst and left a dangling reference.
Fix it.

Fixes: 151f4e2b ("docs: power: convert docs to ReST and rename to *.rst")
Cc: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Len Brown <len.brown@intel.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>