efi: Use device_get_uclass_id() where appropriate

Use this function rather than following the pointers, since it is there
for this purpose.

Add the uclass name to the debug call at the end of dp_fill() since it is
quite useful.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>