lookup: exit on error in make_modname()

Actually exit on strdup error instead of just printing a warning message
in make_modname().

Found by covscan, see issue #984 for full log.

Signed-off-by: Artem Savkov <asavkov@redhat.com>

kpatch-build/lookup.c

@@ -185,7 +185,7 @@ static char *make_modname(char *modname)
 
 	name = strdup(basename(modname));
 	if (!name)
-		perror("strdup");
+		ERROR("strdup");
 
 	cur = name; /* use cur as tmp */
 	while (*cur != '\0') {