[flashrom] [PATCH] Fix Winbond W25X{10, 20, 40, 80} incorrect erase blocks

[Sean Nelson]

Fix erase blocks for Winbond W25X* SPI chips. The Winbond W25X10 and 
related chips only have 4k and 64k blocks and only accept erase 
commands: 20h, d8h, and c7h.

Signed-off-by: Sean Nelson