ufs_disk_close.3: Correct include header macro

This manual used the library macro to mark up a header file, causing
pollution in the apropos database for libraries, as well as omission
from the apropos database for headers. This also renders differently,
enclosing the header in angle brackets.

MFC after: 3 days

(cherry picked from commit 456ae9820823fcd078746318620925792f112c9a)