Device-tree rules require that aliases use a hyphen rather than a
underscore. Update the uclass name to fit with this.

This allows device-tree aliases to be used to refer to cros-ec devices,
for example:

	aliases {
	    cros-ec0 = &ec;
	    cros-ec1 = &pd;
	};

Series-changes: 2
- Update the commit message to explain the implications on aliases

Signed-off-by: Simon Glass <sjg@chromium.org>