gateware/firmware: Match rx/tx tick order in register with doc

The documentation always had the rRX tick in the LSB which
is consistent with having the RX units before TX.

They can be read as 16 bit value anyway so there isn't any
performance impact.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/firmware/ice40-riscv/icE1usb/misc.c b/firmware/ice40-riscv/icE1usb/misc.c
index 9ceb8c6..6f40fd4 100644
--- a/firmware/ice40-riscv/icE1usb/misc.c
+++ b/firmware/ice40-riscv/icE1usb/misc.c
@@ -18,8 +18,8 @@
 	uint32_t e1_led;
 	uint32_t _rsvd;
 	struct {
-		uint16_t tx;
 		uint16_t rx;
+		uint16_t tx;
 	} e1_tick[2];
 	uint32_t gps;
 	uint32_t time;