firewire: don't panic on invalid AR request buffer

BUG() at this place is wrong. (Unless if the low level driver would
already do higher-level input validation of incoming request headers.)

Invalid incoming requests or bugs in the controller which corrupt the
AR-req buffer needlessly crashed the box because this is run in tasklet
context.

Signed-off-by: Stefan Richter <[e-mail]>

drivers/firewire/fw-transaction.c

···
 		break;
 
 	default:
-		BUG();
+		fw_error("ERROR - corrupt request received - %08x %08x %08x\n",
+			 p->header[0], p->header[1], p->header[2]);
 		return NULL;
 	}