Bump to KhronosGroup/SPIRV-Cross@bccaa94d (#14606)

To pick up several SPIR-V to MSL conversion fixes.
diff --git a/third_party/spirv_cross b/third_party/spirv_cross
index 3550a54..bccaa94 160000
--- a/third_party/spirv_cross
+++ b/third_party/spirv_cross
@@ -1 +1 @@
-Subproject commit 3550a54ae01b295c40ce972d951b420b388b9401
+Subproject commit bccaa94db814af33d8ef05c153e7c34d8bd4d685