Use use instead of extern

Author: Sh3Rm4n

examples/adc.rs

@@ -3,7 +3,7 @@
 
 //! Example usage for ADC on STM32F303
 
-extern crate panic_semihosting;
+use panic_semihosting as _;
 
 use cortex_m_rt::entry;
 use cortex_m_semihosting::hprintln;