drivers/edac: edac_device code tidying

For the file edac_device.c perform some coding style enhancements
Add some function header comments
Made for better readability commands

Signed-off-by: Douglas Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>