libnvme: git submodule update

Pull in changes to fixup loop device handling.

diff --git a/libnvme b/libnvme
index 7bbad82cd35374d1975d92aa82aa11536eaaf0f0..278aba093e64bb89d8e471ddf1d0c83b0ff5b2f5 160000 (submodule)
--- a/libnvme
+++ b/libnvme
@@ -1 +1 @@
-Subproject commit 7bbad82cd35374d1975d92aa82aa11536eaaf0f0
+Subproject commit 278aba093e64bb89d8e471ddf1d0c83b0ff5b2f5