block: Catch simultaneous usage of options and their aliases

block: Catch simultaneous usage of options and their aliases

While thinking about precedence of conflicting block device options from
different sources, I noticed that you can specify both an option and its
legacy alias at the same time (e.g. readonly=on,read-only=off). Rather
than specifying the order of precedence, we should simply forbid such
combinations.

Signed-off-by: Kevin Wolf <[email protected]>
Reviewed-by: Benoît Canet <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>