Set audio player to width: 100% and avoid breaking the layout in iOS when we fall back to a link.

Merges [24948] to the 3.6 branch.

props markjaquith, davidjlaietta.
fixes #24896.



git-svn-id: https://core.svn.wordpress.org/branches/3.6@24949 1a063a9b-81f0-0310-95a4-ce76da25c4cd