Fix incorrect use of == instead of =.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

src/fw.c

@@ -851,7 +851,7 @@ handle_arm_request(raw1394handle_t handle, struct address_closure *ac,
 
 	rrb = malloc(sizeof *rrb + in_length + response.length);
 	if (rrb == NULL) {
-		errno == ENOMEM;
+		errno = ENOMEM;
 		return -1;
 	}