Writing to 65c22 IFR (reg 13) clears any flag specified in the written byte (#347)

* Writing to 65c22 IFR clears any flag specified in the written byte

This matches the behavior of the hardware. Previous implementation
only cleared CA2 or CB2 flags, and then only if they were configured
as independent interrupts.

* Avoid touching IFR7 on write

* remove unused variable

---------

Co-authored-by: mooinglemur <[email protected]>

Author: catharinejm

src/via.c

@@ -98,7 +98,6 @@ via_read(via_t *via, uint8_t reg, bool debug)
 static void
 via_write(via_t *via, uint8_t reg, uint8_t value)
 {
-	uint8_t pcr;
 	switch (reg) {
 		case 0: // ORB
 			via_clear_prb_irqs(via);
@@ -132,13 +131,7 @@ via_write(via_t *via, uint8_t reg, uint8_t value)
 			via->registers[10] = value;
 			break;
 		case 13: // IFR
-			pcr = via->registers[12];
-			if ((value & 0x01) && ((pcr & 0b00001010) == 0b00000010)) {
-				via->registers[13] &= ~0x01;
-			}
-			if ((value & 0x08) && ((pcr & 0b10100000) == 0b00100000)) {
-				via->registers[13] &= ~0x08;
-			}
+			via->registers[13] &= ~(value & 0x7f);
 			break;
 		case 14: // IER
 			if (value & 0x80) {