[pic8259] Fix definitions for "read IRR" and "read ISR" commands

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/include/pic8259.h

 
 /* Register command values */
 #define OCW3_ID 0x08
-#define OCW3_READ_IRR 0x03
-#define OCW3_READ_ISR 0x02
+#define OCW3_READ_IRR 0x02
+#define OCW3_READ_ISR 0x03
 #define ICR_EOI_NON_SPECIFIC 0x20
 #define ICR_EOI_NOP 0x40
 #define ICR_EOI_SPECIFIC 0x60