Bring `bp_get_blog_last_active()` up to parity with `bp_get_member_last_active()` for 2.1.

Also fix speeling error in `bp_get_member_last_active()`.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8998 cdf35c40-ae34-48e0-9cc9-0c9da1808c22