docs: kdoc: use self.entry.parameterlist directly in check_sections()

docs: kdoc: use self.entry.parameterlist directly in check_sections()

Callers of check_sections() join parameterlist into a single string, which
is then immediately split back into the original list.  Rather than do all
that, just use parameterlist directly in check_sections().

Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>