Change the type of the first argument to the I/O emulation handlers to
'struct vm *'. Previously it used to be a 'void *' but there is no reason
to hide the actual type from the handler.

Discussed with:	tychon
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273706 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f