mtd: spinand: winbond: Ignore the last ID characters

The last 4 characters in Winbond's branding indicate:
- the package type (ZE/SF/TB),
- the temperature grade (I/J),
- special options, typically the continuous read vs. page read feature
  support and its default (G/T/F/R),

None of these information impact us, at the software level (well, the
continuous read mode by default is impacting, but is already handled
gracefully by disabling it in the initialization phase), so let's get
rid of it.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Link: https://lore.kernel.org/linux-mtd/20241009125002.191109-4-miquel.raynal@bootlin.com