spdk: pick up spdk v20.07

NVMe-RBD gateway utility uses SPDK's RBD bdev backend and NVMe-oF
transport support. so let's use the latest SPDK release for these
features.

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/spdk b/src/spdk
index 06d09c1108b16197ea985ae4d67867ed672a1e18..1a527e501f810e2b39b9862c96f3e8bdc465db80 160000 (submodule)
--- a/src/spdk
+++ b/src/spdk
@@ -1 +1 @@
-Subproject commit 06d09c1108b16197ea985ae4d67867ed672a1e18
+Subproject commit 1a527e501f810e2b39b9862c96f3e8bdc465db80