Fix 'function declaration isn't a prototype' warning.

Pointed by:	ian
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271485 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Simplify vntype_to_kinfo() by returning when the desired value is found
instead of breaking out of the loop and then immediately checking the loop
index so that if it was broken out of the proper value can be returned.

While here, use nitems().


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271486 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f