[PATCH] md: Change case of raid level reported in sys/mdX/md/level

I had thought that keeping the reported tail level clearly different
from the module name was a good idea, but I've changed my mind.

'raid5' is better and probably less confusing than 'RAID-5'.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>