shader_bytecode: Make operator== and operator!= of IpaMode const qualified

These don't affect the state of the struct and can be const member
functions.

src/video_core/engines/shader_bytecode.h

@@ -5,9 +5,8 @@
 #pragma once
 
 #include <bitset>
-#include <cstring>
-#include <map>
 #include <string>
+#include <tuple>
 #include <vector>
 
 #include <boost/optional.hpp>
@@ -321,11 +320,13 @@ enum class IpaSampleMode : u64 { Default = 0, Centroid = 1, Offset = 2 };
 struct IpaMode {
     IpaInterpMode interpolation_mode;
     IpaSampleMode sampling_mode;
-    inline bool operator==(const IpaMode& a) {
-        return (a.interpolation_mode == interpolation_mode) && (a.sampling_mode == sampling_mode);
+
+    bool operator==(const IpaMode& a) const {
+        return std::tie(interpolation_mode, sampling_mode) ==
+               std::tie(a.interpolation_mode, a.sampling_mode);
     }
-    inline bool operator!=(const IpaMode& a) {
-        return !((*this) == a);
+    bool operator!=(const IpaMode& a) const {
+        return !operator==(a);
     }
 };