mtd: rawnand: Fix nand_choose_best_timings() on unsupported interface

When the NV-DDR interface is not supported by the NAND chip,
the value of onfi->nvddr_timing_modes is 0. In this case,
the best_mode variable value in nand_choose_best_nvddr_timings()
is -1. The last for-loop is skipped and the function returns an
uninitialized value.
If this returned value is 0, the nand_choose_best_sdr_timings()
is not executed and no 'best timing' are set. This leads the host
controller and the NAND chip working at default mode 0 timing
even if a better timing can be used.

Fix this uninitialized returned value.

nand_choose_best_sdr_timings() is pretty similar to
nand_choose_best_nvddr_timings(). Even if onfi->sdr_timing_modes
should never be seen as 0, nand_choose_best_sdr_timings() returned
value is fixed.

Fixes: a9ecc8c8 ("mtd: rawnand: Choose the best timings, NV-DDR included")
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211119150316.43080-3-herve.codina@bootlin.com