move fpga repo to git@ from https

.gitmodules

@@ -18,4 +18,4 @@
 	url = git@github.com:ucb-bar/berkeley-hardfloat.git
 [submodule "fpga-zynq"]
 	path = fpga-zynq
-	url = https://github.com/ucb-bar/fpga-zynq.git
+	url = git@github.com:ucb-bar/fpga-zynq.git