regroup assignment-related diagnostics, fix a mistake in one.

llvm-svn: 45558
diff --git a/clang/Sema/SemaExpr.cpp b/clang/Sema/SemaExpr.cpp
index 68c301a..bab7d3d 100644
--- a/clang/Sema/SemaExpr.cpp
+++ b/clang/Sema/SemaExpr.cpp
@@ -2254,7 +2254,7 @@
            argExpr->getSourceRange());
       break;
     case CompatiblePointerDiscardsQualifiers:
-      Diag(l, diag::ext_typecheck_passing_discards_qualifiers,
+      Diag(l, diag::ext_typecheck_sending_discards_qualifiers,
            rhsType.getAsString(), lhsType.getAsString(),
            argExpr->getSourceRange());
       break;