[PATCH] vt: Decrement ref count of the VT backend on deallocation

When a VT is newly allocated, the module reference count of the backend
will be incremented.  This should be balanced by a module_put() when this
VT is deallocated.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>