Enable stm32f3/critical-section for examples

Author: usbalbin

Cargo.toml

@@ -56,6 +56,7 @@ panic-rtt-target = { version = "0.1.2", features = ["cortex-m"] }
 panic-semihosting = "0.6.0"
 rtt-target = { version = "0.4.0" }
 systick-monotonic = "1.0"
+stm32f3 = { version = "0.17.0", package = "stm32f3-staging", features = ["critical-section"], default-features = false }
 usb-device = "0.3.1"
 usbd-serial = "0.2.0"