mtd: spi-nor: simplify spi_nor_get_flash_info()

Rework spi_nor_get_flash_info() to make it look more straight forward
and esp. don't return early. The latter is a preparation to check for
deprecated flashes.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://lore.kernel.org/r/20240603134055.1859863-1-mwalle@kernel.org