mtd: nand_base: Removed unnecessary cleaning "onfi_version" variable

Variable "onfi_version" is already set to zero before nand_flash_detect_onfi()
call, so additional cleaning is not necessary.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>