mtd: nand: fixup kerneldoc, rename parameter

First, the function argument is 'offset' not 'column'.

Second, the 'data_buf' name is inconsistent with the rest of this file.
Just use 'buf'.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Gupta, Pekon <pekon@ti.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>