regulator: get_status() grows kerneldoc

Add kerneldoc for the new get_status() message.  Fix the existing
kerneldoc for that struct in two ways:

 (a) Syntax, making sure parameter descriptions immediately
     follow the one-line struct description and that the first
     blank lines is before any more expansive description;
 (b) Presentation for a few points, to highlight the fact that
     the previous "get" methods exist only to report the current
     configuration, not to display actual status.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>