Use modify instead of write for HSI14 clock setup

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

CHANGELOG.md

@@ -17,6 +17,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Updated the ADC code to use variants added in stm32-rs v0.6.0 - @HarkonenBade
 - Improved serial `write_str` implementation
 
+### Fixed
+
+- Fixed ADC use trampling over the HSI48 clock settings
+
 ## [v0.12.0] - 2019-01-13
 
 ### Added

src/adc.rs

@@ -561,7 +561,7 @@ impl Adc {
 
     fn select_clock(&mut self, rcc: &mut Rcc) {
         rcc.regs.apb2enr.modify(|_, w| w.adcen().enabled());
-        rcc.regs.cr2.write(|w| w.hsi14on().on());
+        rcc.regs.cr2.modify(|_, w| w.hsi14on().on());
         while rcc.regs.cr2.read().hsi14rdy().is_not_ready() {}
     }