vm_page.h: page busy macro fixups

Minor changes to:

• delete extraneous trailing semicolons from macro definitions, and
• correct spelling of "busying" in panic messages

Submitted by: Ryan Libby <rlibby@gmail.com>
Reviewed by: alc, kib
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D4577