mtd: nand: make reads using MTD_OOB_RAW affect only ECC validation

This changes the behavier of MTD_OOB_RAW. It used to read both OOB and 
data to the data buffer, however you would still need to specify the 
dummy oob buffer.

This is only used in one place, but makes it hard to read data+oob 
without ECC test, thus I removed that behavier, and fixed the user.

Now MTD_OOB_RAW behaves just like MTD_OOB_PLACE, but doesn't do ECC 
validation

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>