fixed SPIR-V compilation error with unmodified variables

Change-Id: I22981a60c21a2e16d41d69c53e099f221a202a58
Reviewed-on: https://skia-review.googlesource.com/11000
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/SkSLParser.cpp b/src/sksl/SkSLParser.cpp
index 1004de8..cdbf25e 100644
--- a/src/sksl/SkSLParser.cpp
+++ b/src/sksl/SkSLParser.cpp
@@ -498,7 +498,7 @@
 
 /* modifiers type IDENTIFIER (LBRACKET INT_LITERAL RBRACKET)? */
 std::unique_ptr<ASTParameter> Parser::parameter() {
-    Modifiers modifiers = this->modifiersWithDefaults(Modifiers::kIn_Flag);
+    Modifiers modifiers = this->modifiersWithDefaults(0);
     std::unique_ptr<ASTType> type = this->type();
     if (!type) {
         return nullptr;