xnvme: change gitmodule-remote

The xNVMe repository has moved from "OpenMPDK/xNVMe" to "xnvme/xnvme,"
thus changing the git-module remote to reflect this.

GitHub does provide redirection; however, eventually, it could break,
and when doing so, it is better to have the module pointing to the "new"
location well in advance.

Change-Id: I5e32914dbfab6202446ec80c3d5764e8ebc3d6d4
Signed-off-by: Simon A. F. Lund <simon.lund@samsung.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/23152


Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <jim.harris@samsung.com>
Reviewed-by: Karl Bonde Torp <k.torp@samsung.com>