ARM: dts: stm32: Repair I2C2 operation on AV96

The I2C2 uses different pinmux on AV96, use correct pinmux and
also add comments about the I2C being present on the "low-speed"
expansion connector X6.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp157a-avenger96.dts

@@ -164,7 +164,7 @@ phy0: ethernet-phy@7 {
 	};
 };
 
-&i2c1 {
+&i2c1 {	/* X6 I2C1 */
 	pinctrl-names = "default";
 	pinctrl-0 = <&i2c1_pins_b>;
 	i2c-scl-rising-time-ns = <185>;
@@ -174,9 +174,9 @@ &i2c1 {
 	/delete-property/dma-names;
 };
 
-&i2c2 {
+&i2c2 {	/* X6 I2C2 */
 	pinctrl-names = "default";
-	pinctrl-0 = <&i2c2_pins_b1 &i2c2_pins_b2>;
+	pinctrl-0 = <&i2c2_pins_c>;
 	i2c-scl-rising-time-ns = <185>;
 	i2c-scl-falling-time-ns = <20>;
 	status = "okay";