ideapad-laptop: Constify DMI table for real!

ideapad-laptop: Constify DMI table for real!

This is a follow-up patch to commit 49458e83082d ("ideapad-laptop:
Constify DMI table and other r/o variables") to do what its commit
message says. The actual commit differs from the patch posted at
https://www.mail-archive.com/[email protected]/msg05340.html
significantly, probably due to a bad merge conflict resolution. Fix up
the mess and constify the DMI table for real and fix the bogus
double-const of ideapad_rfk_data[].

Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Mathias Krause <[email protected]>
Cc: Matthew Garrett <[email protected]>
Cc: Ike Panhc <[email protected]>
Signed-off-by: Darren Hart <[email protected]>