platform: inhibit motor pins and remove output routes

platforms/stm32f7/src/f722/peripherals/usart.rs

@@ -104,6 +104,10 @@ impl Usart1Tx {
     ) -> Result<Self, BaudRateError> {
         let brr = calculate_brr(peripheral_clock_hz, baud)?;
 
+        // Do not inherit a bootloader or earlier image's USART1 kernel-clock
+        // selection. The F722 platform passes PCLK2 when calculating BRR, so
+        // select it explicitly before programming the divisor.
+        rcc.dckcfgr2().modify(|_, write| write.usart1sel().apb2());
         rcc.apb2rstr()
             .modify(|_, write| write.usart1rst().set_bit());
         rcc.apb2rstr()