Fix DMAMUX_SOURCE_LPUARTX settings

The TX and RX values were reversed.
That is for example on Serial1 (LPUART6)
Before we had:
```
```
now we have
```
```
So for example trying to get WS2812Serial library to work was failing, to output anything.

teensy4/imxrt.h

@@ -185,14 +185,14 @@ static inline void attachInterruptVector(enum IRQ_NUMBER_t irq, void (*function)
 #define DMAMUX_SOURCE_FLEXIO1_REQUEST1		0
 #define DMAMUX_SOURCE_FLEXIO2_REQUEST0		1
 #define DMAMUX_SOURCE_FLEXIO2_REQUEST1		1
-#define DMAMUX_SOURCE_LPUART1_RX		2
-#define DMAMUX_SOURCE_LPUART1_TX		3
-#define DMAMUX_SOURCE_LPUART3_RX		4
-#define DMAMUX_SOURCE_LPUART3_TX		5
-#define DMAMUX_SOURCE_LPUART5_RX		6
-#define DMAMUX_SOURCE_LPUART5_TX		7
-#define DMAMUX_SOURCE_LPUART7_RX		8
-#define DMAMUX_SOURCE_LPUART7_TX		9
+#define DMAMUX_SOURCE_LPUART1_TX		2
+#define DMAMUX_SOURCE_LPUART1_RX		3
+#define DMAMUX_SOURCE_LPUART3_TX		4
+#define DMAMUX_SOURCE_LPUART3_RX		5
+#define DMAMUX_SOURCE_LPUART5_TX		6
+#define DMAMUX_SOURCE_LPUART5_RX		7
+#define DMAMUX_SOURCE_LPUART7_TX		8
+#define DMAMUX_SOURCE_LPUART7_RX		9
 #define DMAMUX_SOURCE_FLEXCAN3			11
 #define DMAMUX_SOURCE_CSI			12
 #define DMAMUX_SOURCE_LPSPI1_RX			13
@@ -259,14 +259,14 @@ static inline void attachInterruptVector(enum IRQ_NUMBER_t irq, void (*function)
 #define DMAMUX_SOURCE_FLEXIO1_REQUEST3		64
 #define DMAMUX_SOURCE_FLEXIO2_REQUEST2		65
 #define DMAMUX_SOURCE_FLEXIO2_REQUEST3		65
-#define DMAMUX_SOURCE_LPUART2_RX		66
-#define DMAMUX_SOURCE_LPUART2_TX		67
-#define DMAMUX_SOURCE_LPUART4_RX		68
-#define DMAMUX_SOURCE_LPUART4_TX		69
-#define DMAMUX_SOURCE_LPUART6_RX		70
-#define DMAMUX_SOURCE_LPUART6_TX		71
-#define DMAMUX_SOURCE_LPUART8_RX		72
-#define DMAMUX_SOURCE_LPUART8_TX		73
+#define DMAMUX_SOURCE_LPUART2_TX		66
+#define DMAMUX_SOURCE_LPUART2_RX		67
+#define DMAMUX_SOURCE_LPUART4_TX		68
+#define DMAMUX_SOURCE_LPUART4_RX		69
+#define DMAMUX_SOURCE_LPUART6_TX                70
+#define DMAMUX_SOURCE_LPUART6_RX		71
+#define DMAMUX_SOURCE_LPUART8_TX		72
+#define DMAMUX_SOURCE_LPUART8_RX		73
 #define DMAMUX_SOURCE_PXP			75
 #define DMAMUX_SOURCE_LCDIF			76
 #define DMAMUX_SOURCE_LPSPI2_RX			77