mtd: nand: denali: prefix detect_max_banks() with denali_

All functions in this driver are prefixed with denali_
except detect_max_banks().  Rename it for consistency.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>