We must free the variable str.

Spotted by:	clang's static analyzer
Submitted by:	Tom Rix <trix_juniper.net>
Reviewed by:	grehan
MFC after:	4 weeks
Sponsored by:	iXsystems Inc.
Differential Revision:	https://reviews.freebsd.org/D10009

usr.sbin/bhyve/pci_emul.c

@@ -231,8 +231,7 @@ pci_parse_slot(char *opt)
 	si->si_funcs[fnum].fi_param = config;
 
 done:
-	if (error)
-		free(str);
+	free(str);
 
 	return (error);
 }