zfs: cherry-pick lock-inversion patch for zvol_open

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

diff --git a/submodules/zfsonlinux b/submodules/zfsonlinux
index 64e59c5ce93303049a2f822facb35b868aa2268a..531eac33046f7e207226b428e399bcab173b7b6b 160000 (submodule)
--- a/submodules/zfsonlinux
+++ b/submodules/zfsonlinux
@@ -1 +1 @@
-Subproject commit 64e59c5ce93303049a2f822facb35b868aa2268a
+Subproject commit 531eac33046f7e207226b428e399bcab173b7b6b