mtd: nand: Fix timing setup for NANDs that do not support SET FEATURES

Some ONFI NANDs do not support the SET/GET FEATURES commands, which,
according to the spec, is perfectly valid.

On these NANDs we can't set a specific timing mode using the "timing
mode" feature, and we should assume the NAND does not require any setup
to enter a specific timing mode.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Fixes: d8e725dd ("mtd: nand: automate NAND timings selection")
Reported-by: Alexander Dahl <ada@thorsis.com>
Cc: <stable@vger.kernel.org>
Tested-by: Alexander Dahl <ada@thorsis.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>