gateware/icE1usb: Set divider of I2C core to be ~ 400 kHz

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: I1dd4ab34da9d01b599cf9c782e721aaee9b8740d
diff --git a/gateware/icE1usb/rtl/top.v b/gateware/icE1usb/rtl/top.v
index fdf75a1..7762fb0 100644
--- a/gateware/icE1usb/rtl/top.v
+++ b/gateware/icE1usb/rtl/top.v
@@ -316,7 +316,7 @@
 
 	// Controller
 	i2c_master_wb #(
-		.DW(3),
+		.DW(4),
 		.FIFO_DEPTH(0)
 	) i2c_I (
 		.scl_oe  (i2c_scl_oe),