drivers/i2c: it51xxx: Fix build assert to check port number instead of inst

Currently the build assert checks the number of I2C instances as
the available I2C target mode, which is incorrect.
This patch updates the build assert to check the I2C port_num instead,
since IT51xxx only supports I2C target mode on ports 0 to 2.

Signed-off-by: Tim Lin <[email protected]>

Author: GTLin08

drivers/i2c/i2c_ite_it51xxx.c

@@ -1946,8 +1946,9 @@ static int i2c_it51xxx_init(const struct device *dev)
 			     (DT_INST_PROP(inst, clock_frequency) == I2C_BITRATE_FAST) ||          \
 			     (DT_INST_PROP(inst, clock_frequency) == I2C_BITRATE_FAST_PLUS),       \
 		     "Not support I2C bit rate value");                                            \
-	BUILD_ASSERT(!(DT_INST_PROP(inst, target_enable) && (inst > SMB_CHANNEL_C)),               \
-		     "Only instances 0~2 can enable target-enable");                               \
+	BUILD_ASSERT(!(DT_INST_PROP(inst, target_enable) &&                                        \
+		       (DT_INST_PROP(inst, port_num) > SMB_CHANNEL_C)),                            \
+		     "Only ports 0~2 support I2C target mode");                                    \
 	static const struct i2c_it51xxx_config i2c_it51xxx_cfg_##inst = {                          \
 		.i2cbase = DT_REG_ADDR_BY_IDX(DT_NODELABEL(i2cbase), 0),                           \
 		.i2cbase_mapping = DT_REG_ADDR_BY_IDX(DT_NODELABEL(i2cbase), 1),                   \