mtd: spi-nor: core: Update comment about the default flash parameters

s/legacy/default. spi_nor_info_init_params initializes some default
flash parameters and settings that can be overwritten when parsing
SFDP, or by fixup hooks. There's nothing legacy about them, they are
just some default settings, if not otherwise discovered or specified.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20210315055634.17332-1-tudor.ambarus@microchip.com