drivers: serial: uart_sam0: Update to correct bitmask

Update uart_sam0_irq_tx_enable to use the correct INTENSET bitmask.

Signed-off-by: Ron Smith <rockyowl171@gmail.com>
diff --git a/drivers/serial/uart_sam0.c b/drivers/serial/uart_sam0.c
index 9adc8c0..1b5d9ca 100644
--- a/drivers/serial/uart_sam0.c
+++ b/drivers/serial/uart_sam0.c
@@ -740,7 +740,7 @@
 {
 	SercomUsart * const regs = DEV_CFG(dev)->regs;
 
-	regs->INTENSET.reg = SERCOM_USART_INTENCLR_DRE;
+	regs->INTENSET.reg = SERCOM_USART_INTENSET_DRE;
 }
 
 static void uart_sam0_irq_tx_disable(const struct device *dev)