Fix typo in "Entering long mode"
Fix typo in "Entering long mode"

I think there is a typo in the section describing how the P2 mapping is set up. The corresponding code sets _P2_'s third entry.
phil-opp/blog_os,rafalmiel/blog_os,phil-opp/blog_os,phil-opp/blogOS,phil-opp/blog_os,phil-opp/blog_os,phil-opp/blogOS,rafalmiel/blog_os