mtd: rawnand: fsmc: Default to autodetect buswidth

mtd: rawnand: fsmc: Default to autodetect buswidth

If you don't specify buswidth 2 (16 bits) in the device
tree, FSMC doesn't even probe anymore:

fsmc-nand 10100000.flash: FSMC device partno 090,
  manufacturer 80, revision 00, config 00
nand: device found, Manufacturer ID: 0x20, Chip ID: 0xb1
nand: ST Micro 10100000.flash
nand: bus width 8 instead of 16 bits
nand: No NAND device found
fsmc-nand 10100000.flash: probe with driver fsmc-nand failed
  with error -22

With this patch to use autodetection unless buswidth is
specified, the device is properly detected again:

fsmc-nand 10100000.flash: FSMC device partno 090,
  manufacturer 80, revision 00, config 00
nand: device found, Manufacturer ID: 0x20, Chip ID: 0xb1
nand: ST Micro NAND 128MiB 1,8V 16-bit
nand: 128 MiB, SLC, erase size: 128 KiB, page size: 2048, OOB size: 64
fsmc-nand 10100000.flash: Using 1-bit HW ECC scheme
Scanning device for bad blocks

I don't know where or how this happened, I think some change
in the nand core.

Cc: stable@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>