jlink_spi: Reduce transfer size

The maximum transfer size is too large for some devices and
results in an USB timeout.

Change-Id: If2c00b1524ec56740bdfe290096c3546cf375d73
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/48379
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Miklós Márton <martonmiklosqdev@gmail.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
1 file changed