disable the default features of the cast dependency

Author: japaric

Cargo.toml

@@ -9,7 +9,11 @@ repository = "https://github.com/japaric/linux-embedded-hal"
 version = "0.1.0"
 
 [dependencies]
-cast = "0.2.2"
 embedded-hal = "0.1.0"
 spidev = "0.3.0"
 sysfs_gpio = "0.5.1"
+
+[dependencies.cast]
+# we don't need the `Error` implementation
+default-features = false
+version = "0.2.2"