mtdnand.rst: group the "::" with previous line

Group the :: with the previous paragraph, in order to make it
visually better when reading as a text file.

While here, replace:
	ored (with means "Covered or adorned with ore or metal")
by:
	OR-ed

To reflect its true meaning.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>