A Centos 6.4 guest will write 0xff to the 8259 mask register before beginning

the proper ICWx initialization sequence. It assumes, probably correctly, that
the boot firmware has done the 8259 initialization.

Since grub-bhyve does not initialize the 8259 this write to the mask register
takes a code path in which 'error' remains uninitialized (ready=0,icw_num=0).

Fix this by initializing 'error' at the start of the function.

sys/amd64/vmm/io/vatpic.c

@@ -591,6 +591,7 @@ vatpic_write(struct vatpic *vatpic, struct atpic *atpic, bool in, int port,
 	int error;
 	uint8_t val;
 
+	error = 0;
 	val = *eax;
 
 	VATPIC_LOCK(vatpic);