Build i2c dma example only for stm32f411,

remove unused transmute from example

Author: SpeedCrash100

Cargo.toml

@@ -406,7 +406,7 @@ required-features = ["tim2"] # stm32f411
 
 [[example]]
 name = "stopwatch-with-ssd1306-and-interrupts-and-dma-i2c"
-required-features = ["tim2"] # stm32f411
+required-features = ["tim2", "stm32f411"] # stm32f411
 
 [[example]]
 name = "analog-stopwatch-with-spi-ssd1306"

examples/stopwatch-with-ssd1306-and-interrupts-and-dma-i2c.rs

@@ -32,13 +32,10 @@ use crate::hal::{
     rcc::{Clocks, Rcc},
     timer::{CounterUs, Event, Timer},
 };
+use core::cell::{Cell, RefCell};
 use core::fmt::Write;
 use core::ops::DerefMut;
 use core::sync::atomic::{AtomicBool, Ordering};
-use core::{
-    cell::{Cell, RefCell},
-    mem::transmute,
-};
 use cortex_m::interrupt::{free, CriticalSection, Mutex};
 use cortex_m_rt::entry;
 use display_interface::{DataFormat, DisplayError, WriteOnlyDataCommand};