i2c: rtl9300: use scoped guard instead of explicit lock/unlock

Use the scoped guard infrastructure which unlocks a mutex automatically
when the guard goes out of scope, instead of explicit lock and unlock.
This simplifies the code and control flow in rtl9300_i2c_smbus_xfer and
removes the need of using goto in error cases to unlock before
returning.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz> # On RTL9302C based board
Tested-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250927101931.71575-8-jelonek.jonas@gmail.com

Author: jonasjelonek

drivers/i2c/busses/i2c-rtl9300.c

@@ -72,6 +72,8 @@ struct rtl9300_i2c {
 	struct mutex lock;
 };
 
+DEFINE_GUARD(rtl9300_i2c, struct rtl9300_i2c *, mutex_lock(&_T->lock), mutex_unlock(&_T->lock))
+
 enum rtl9300_i2c_xfer_type {
 	RTL9300_I2C_XFER_BYTE,
 	RTL9300_I2C_XFER_WORD,
@@ -283,11 +285,11 @@ static int rtl9300_i2c_smbus_xfer(struct i2c_adapter *adap, u16 addr, unsigned s
 	if (addr > 0x7f)
 		return -EINVAL;
 
-	mutex_lock(&i2c->lock);
+	guard(rtl9300_i2c)(i2c);
 
 	ret = rtl9300_i2c_config_chan(i2c, chan);
 	if (ret)
-		goto out_unlock;
+		return ret;
 
 	xfer.dev_addr = addr & 0x7f;
 	xfer.write = (read_write == I2C_SMBUS_WRITE);
@@ -324,20 +326,14 @@ static int rtl9300_i2c_smbus_xfer(struct i2c_adapter *adap, u16 addr, unsigned s
 		break;
 	default:
 		dev_err(&adap->dev, "Unsupported transaction %d\n", size);
-		ret = -EOPNOTSUPP;
-		goto out_unlock;
+		return -EOPNOTSUPP;
 	}
 
 	ret = rtl9300_i2c_prepare_xfer(i2c, &xfer);
 	if (ret)
-		goto out_unlock;
-
-	ret = rtl9300_i2c_do_xfer(i2c, &xfer);
-
-out_unlock:
-	mutex_unlock(&i2c->lock);
+		return ret;
 
-	return ret;
+	return rtl9300_i2c_do_xfer(i2c, &xfer);
 }
 
 static u32 rtl9300_i2c_func(struct i2c_adapter *a)