wireless: fix enabling channel 12 for custom regulatory domain

wireless: fix enabling channel 12 for custom regulatory domain

Commit 224b3d0c7689 ("Revert "cfg80211: Use 5MHz bandwidth by
default when checking usable channels"") fixed a broken
regulatory (leaving channel 12 open for AP where not permitted).
Apply a similar fix to custom regulatory domain processing.

Signed-off-by: Cathy Luo <xiaohua.luo@nxp.com>
Signed-off-by: Ganapathi Bhat <ganapathi.bhat@nxp.com>
Link: https://lore.kernel.org/r/1576836859-8945-1-git-send-email-ganapathi.bhat@nxp.com
[reword commit message, fix coding style, add a comment]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>