docs: kdoc: properly handle empty enum arguments

docs: kdoc: properly handle empty enum arguments

Depending on how the enum proto is written, a comma at the end
may incorrectly make kernel-doc parse an arg like " ".

Strip spaces before checking if arg is empty.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <4182bfb7e5f5b4bbaf05cee1bede691e56247eaf.1773074166.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <640784283d52c5fc52ea597344ecd567e2fb6e22.1773770483.git.mchehab+huawei@kernel.org>