Make 11-usart example code safe again

Updating stm32f3xx-hal makes accessing these registers safe as it should
be.

Author: sirhcel

src/11-usart/examples/buffer-overrun-txe.rs

@@ -16,7 +16,7 @@ fn main() -> ! {
 
         usart1
             .tdr
-            .write(|w| unsafe { w.tdr().bits(u16::from(*byte)) });
+            .write(|w| w.tdr().bits(u16::from(*byte)));
     }
     let elapsed = instant.elapsed(); // in ticks
 

src/11-usart/examples/buffer-overrun.rs

@@ -12,7 +12,7 @@ fn main() -> ! {
     for byte in b"The quick brown fox jumps over the lazy dog.".iter() {
         usart1
             .tdr
-            .write(|w| unsafe { w.tdr().bits(u16::from(*byte)) });
+            .write(|w| w.tdr().bits(u16::from(*byte)));
     }
 
     loop {}

src/11-usart/examples/echo.rs

@@ -25,7 +25,7 @@ fn main() -> ! {
                     while usart1.isr.read().txe().bit_is_clear() {}
                     usart1
                         .tdr
-                        .write(|w| unsafe { w.tdr().bits(u16::from(*byte)) });
+                        .write(|w| w.tdr().bits(u16::from(*byte)));
                 }
 
                 break;
@@ -38,7 +38,7 @@ fn main() -> ! {
                     while usart1.isr.read().txe().bit_is_clear() {}
                     usart1
                         .tdr
-                        .write(|w| unsafe { w.tdr().bits(u16::from(*byte)) });
+                        .write(|w| w.tdr().bits(u16::from(*byte)));
                 }
 
                 break;