mtd: nand: remove kerneldoc for removed function parameter

The 'getchip' parameter is gone as of commit 9f3e0429 ("mtd: nand:
don't select chip in nand_chip's block_bad op"), so kill the doc with
it.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>