mtd: spi-nor: refine Spansion S25FL512S ID

Spansion S25FL512S ID is erroneously using 5-byte JEDEC ID, while the chip
family ID is stored in the 6th byte. Due to using only 5-byte ID, it's also
covering S25FS512S and now that we have added 6-byte ID for that chip, we
can convert S25FL512S to using a proper 6-byte ID as well...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>