mtd: denali: detect the number of banks before resetting NAND

Commit c89eeda810f0ec4f0eee0206ebb79e476df9f83e (mtd: denali: detect the
number of banks) introduced runtime detection of the number of banks.

However, denali_nand_reset() uses uses denanli_nand_info::max_banks so
we need to detect the maximum number of banks before doing the reset.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>