mtd: spi-nor: spansion: slightly rework control flow in late_init()

Don't return early when the flash is smaller than or equal to 16MiB. We
need to be able to register hooks for all sizes of flashes. This also has
the benefit that it increases the readability of the code because the
action, i.e. registering the fixups, is connected to the condition, i.e.
flashes larger than 16MiB.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Tested-by: Pratyush Yadav <p.yadav@ti.com> # on mt35xu512aba, s28hs512t
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220223134358.1914798-28-michael@walle.cc