Quickfix for broken writes on FT2232H based programmers.

Not sure if this is the final/correct fix, but for now it definately
fixes writes on FT2232H hardware. I have tested this on both, the
DLP Design DLP-USB1232H, and the openbiosprog-spi hardware. 

Thanks to Joshua Roys <roysjosh@gmail.com> for the hint on IRC.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>

Index: ft2232_spi.c
===================================================================
--- ft2232_spi.c	(Revision 1146)
+++ ft2232_spi.c	(Arbeitskopie)
@@ -195,7 +195,7 @@
 		msg_perr("Unable to set latency timer\n");
 	}
 
-	if (ftdi_write_data_set_chunksize(ftdic, 512)) {
+	if (ftdi_write_data_set_chunksize(ftdic, 256)) {
 		msg_perr("Unable to set chunk size\n");
 	}