docs: update sysfs-platform_profile.rst reference

docs: update sysfs-platform_profile.rst reference

The file name: Documentation/ABI/testing/sysfs-platform_profile.rst
should be, instead: Documentation/userspace-api/sysfs-platform_profile.rst.

Update its cross-reference accordingly.

Fixes: a2ff95e018f1 ("ACPI: platform: Add platform profile support")
Fixes: 8e0cbf356377 ("Documentation: Add documentation for new platform_profile sysfs attribute")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mark Pearson <markpearson@lenovo.com>
Link: https://lore.kernel.org/r/295089effd8353578b9725c61c0453d920978d72.1621413933.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>