In r340042 an attempt to quiet coverity warning cid 1305412 was overdone.

nopt is the only allocated space,
xopt and cp are aliases into that allocated space.
Remove the 2 unneeded free's

Reported by:	Patrick Mooney (@pmooney_pfmooney.com)
Reviewed by:	jhb (maintainer), Patrick Mooney (joyent/illumos)
Approved by:	bde (mentor)
CID:		1305412
MFC after:	3 days
MFC with:	340042
Differential Revision:	https://reviews.freebsd.org/D19200

usr.sbin/bhyve/block_if.c

@@ -576,8 +576,6 @@ blockif_open(const char *optstr, const char *ident)
 err:
 	if (fd >= 0)
 		close(fd);
-	free(cp);
-	free(xopts);
 	free(nopt);
 	return (NULL);
 }