ft2232_spi.c: change the chunksize from 256 to 270

This is to really make use of page write time advantage.
Because the Chunksize must be 256Byte raw data plus the address and cmd bytes.

For details check:
https://mail.coreboot.org/hyperkitty/list/flashrom@flashrom.org/message/W2HULJTDPHWPBZY6MLM6TGT7RTHSGHON/

Signed-off-by: Simon Buhrow <simon.buhrow@posteo.de>
Change-Id: Iac067a23025e9df053ab9cd4e82a98de70046c18
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/39632
Original-Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Original-Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/71305
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/ft2232_spi.c b/ft2232_spi.c
index d63aa8d..ee19eef 100644
--- a/ft2232_spi.c
+++ b/ft2232_spi.c
@@ -386,7 +386,7 @@
 		msg_perr("Unable to set latency timer (%s).\n", ftdi_get_error_string(ftdic));
 	}
 
-	if (ftdi_write_data_set_chunksize(ftdic, 256)) {
+	if (ftdi_write_data_set_chunksize(ftdic, 270)) {
 		msg_perr("Unable to set chunk size (%s).\n", ftdi_get_error_string(ftdic));
 	}