stm32/mpbthciport: Fix initial baudrate to use provided value.

Fixes bug introduced in the recent bffb71f5

ports/stm32/mpbthciport.c

@@ -196,7 +196,7 @@ int mp_bluetooth_hci_uart_init(uint32_t port, uint32_t baudrate) {
     MP_STATE_PORT(pyb_uart_obj_all)[mp_bluetooth_hci_uart_obj.uart_id - 1] = &mp_bluetooth_hci_uart_obj;
 
     // Initialise the UART.
-    uart_init(&mp_bluetooth_hci_uart_obj, 115200, UART_WORDLENGTH_8B, UART_PARITY_NONE, UART_STOPBITS_1, UART_HWCONTROL_RTS | UART_HWCONTROL_CTS);
+    uart_init(&mp_bluetooth_hci_uart_obj, baudrate, UART_WORDLENGTH_8B, UART_PARITY_NONE, UART_STOPBITS_1, UART_HWCONTROL_RTS | UART_HWCONTROL_CTS);
     uart_set_rxbuf(&mp_bluetooth_hci_uart_obj, sizeof(hci_uart_rxbuf), hci_uart_rxbuf);
 
     // Add IRQ handler for IDLE (i.e. packet finished).