Unbreak switchplate/southpaw_65 after qmk#16277 (qmk#20015)

Apparently the changes done in qmk#16277 swapped the values read from the
PCA9555 expanders by mistake, which resulted in mixed up matrix columns.
Fix the chip and register addresses to match the original code.

Author: sigprof

keyboards/switchplate/southpaw_65/matrix.c

@@ -54,9 +54,9 @@ static uint32_t read_cols(void) {
     uint8_t state_1 = 0;
     uint8_t state_2 = 0;
     uint8_t state_3 = 0;
-    pca9555_readPins(IC2, PCA9555_PORT0, &state_1);
-    pca9555_readPins(IC2, PCA9555_PORT1, &state_2);
-    pca9555_readPins(IC1, PCA9555_PORT1, &state_3);
+    pca9555_readPins(IC1, PCA9555_PORT1, &state_1);
+    pca9555_readPins(IC2, PCA9555_PORT0, &state_2);
+    pca9555_readPins(IC2, PCA9555_PORT1, &state_3);
 
     uint32_t state = ((((uint32_t)state_3 & 0b01111111) << 12) | ((uint32_t)state_2 << 4) | (((uint32_t)state_1 & 0b11110000) >> 4));
     return ~state;