mtd: spi-nor-core: Do not make invalid quad enable fatal

The Micron MT35XU512ABA flash does not support the quad enable bit. But
instead of programming the Quad Enable Require field to 000b ("Device
does not have a QE bit"), it is programmed to 111b ("Reserved").

While this is technically incorrect, it is not reason enough to abort
BFPT parsing. Instead, continue BFPT parsing assuming there is no quad
enable bit present.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>