sys/dev/xen/blkfront/blkfront.c:
	Remove local, and incorrect, definition for the value of an invalid
	grant reference.

	Extract ring cleanup code into xbd_free_ring() function for
	symetry with xbd_alloc_ring().  This process also eliminated
	an initialized but unused variable.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 week
sys/dev/xen/blkfront/blkfront.c:
	Remove dead code.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 week