dm: Tidy up four minor code nits

There is a spelling mistake and two functions are missing comments
altogether. Also the flags declaration is correct, but doesn't follow
style. Finally, the uclass_get_device() function has some errors in
its documentation.

Fix these problems.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek Vasut <marex@denx.de>