Point xpm to our internal mirror that has floating patches

Author: nathanaelhuffman

.gitmodules

@@ -3,7 +3,7 @@
 	url = https://github.com/facebook/buck2-prelude.git
 [submodule "vnd/xpm/xpm_vhdl"]
 	path = vnd/xpm/xpm_vhdl
-	url =  https://github.com/fransschreuder/xpm_vhdl.git
+	url = https://github.com/oxidecomputer/xpm_vhdl.git
 [submodule "vnd/cobble"]
 	path = vnd/cobble
 	url = https://github.com/oxidecomputer/cobble-build.git