set moder::ALTERNATE last when configuring pins to AF modes.

- as per STM32F4xx_hal's impl

embassy-stm32/src/gpio.rs

@@ -310,9 +310,6 @@ pub(crate) mod sealed {
         unsafe fn set_as_af(&self, af_num: u8, af_type: OutputType) {
             let pin = self._pin() as usize;
             let block = self.block();
-            block
-                .moder()
-                .modify(|w| w.set_moder(pin, vals::Moder::ALTERNATE));
             block
                 .afr(pin / 8)
                 .modify(|w| w.set_afr(pin % 8, vals::Afr(af_num)));
@@ -327,6 +324,10 @@ pub(crate) mod sealed {
             block
                 .pupdr()
                 .modify(|w| w.set_pupdr(pin, vals::Pupdr::FLOATING));
+
+            block
+                .moder()
+                .modify(|w| w.set_moder(pin, vals::Moder::ALTERNATE));
         }
 
         unsafe fn set_as_analog(&self) {