docs: generic-counter.rst: fix broken references for ABI file

There are two references to the generic counter ABI, with was added
on a separate patch. Both point to a non-existing file.

Fix them.

Fixes: ea2b23b8 ("counter: Documentation: Add Generic Counter sysfs documentation")
Fixes: 09e7d4ed

 ("docs: Add Generic Counter interface documentation")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>