drivers: pinctrl: silabs: Fix multiple analogue bus allocation on same port

Fix ABUS allocation if both EVEN and ODD busses are used for the
same port. The initialisation loop would incorrectly overwrite
entire GPIO_nBUSALLOC when iterating the pinctrl array, must do
a read/mask/update/write sequence.

Signed-off-by: Jonny Gellhaar <jonny.gellhaar@prevas.se>

Author: gellhaar

drivers/pinctrl/pinctrl_silabs_dbus.c

@@ -24,8 +24,12 @@ int pinctrl_configure_pins(const pinctrl_soc_pin_t *pins, uint8_t pin_cnt, uintp
 		if (pins[i].en_bit == SILABS_PINCTRL_ANALOG) {
 			enable_reg = DT_INST_REG_ADDR_BY_NAME(0, abus) +
 				     (pins[i].base_offset * sizeof(mem_addr_t));
-			sys_write32(FIELD_PREP(ABUS_MASK(pins[i].mode), pins[i].route_offset),
-				    enable_reg);
+			/* Read-modify-write. */
+			uint32_t reg_val = sys_read32(enable_reg);
+
+			reg_val &= ~ABUS_MASK(pins[i].mode);
+			reg_val |= FIELD_PREP(ABUS_MASK(pins[i].mode), pins[i].route_offset);
+			sys_write32(reg_val, enable_reg);
 			continue;
 		}