mtd: Make SM_FTL depend on MTD_NAND

Randy Dunlap observed a build problem with the following config:

CONFIG_SM_FTL=y
CONFIG_SM_FTL_MUSEUM=y

CONFIG_MTD_NAND=m

The ECC calculation routines are then built as a module, but referenced
by the sm_ftl code in the kernel, resulting in a build failure. The
simple fix is to make CONFIG_SM_FTL depend on MTD_NAND unconditionally
-- it's pointless without hardware support anyway.

Fix some typos which Randy pointed out, too.

Reported-By: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>