MTD: kernel-doc fixes + additions

Fix some kernel-doc typos/spellos.
Use kernel-doc syntax in places where it was almost used.
Correct/add struct, struct field, and function param names where needed.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>