mtd: spi-nor: Fix read SFDP data in dual parallel mode

mtd: spi-nor: Fix read SFDP data in dual parallel mode

Reading the SFDP data is broken in two ways in dual parallel mode in the
current implementation.

1) It reads the data interleaved from both chips, which results in data
that can not be parsed. Since both chips have to be identical for dual
parallel mode the SFDP data will also be identical. So only read the data
from one of the chips.

2) The page, erase and chip size are not update to reflect that they should
be twice as large in dual parallel mode. Fix this by moving the update of
those parameter after running the SFDP detection rather than doing it
before.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>