[AMDGPU] Silence gcc 7 warnings

Differential Revision: https://reviews.llvm.org/D59330

llvm-svn: 356100
diff --git a/llvm/lib/Target/AMDGPU/SIPeepholeSDWA.cpp b/llvm/lib/Target/AMDGPU/SIPeepholeSDWA.cpp
index 547fad1..dc2e9dc 100644
--- a/llvm/lib/Target/AMDGPU/SIPeepholeSDWA.cpp
+++ b/llvm/lib/Target/AMDGPU/SIPeepholeSDWA.cpp
@@ -347,8 +347,8 @@
   if (Abs || Neg) {
     assert(!Sext &&
            "Float and integer src modifiers can't be set simulteniously");
-    Mods |= Abs ? SISrcMods::ABS : 0;
-    Mods ^= Neg ? SISrcMods::NEG : 0;
+    Mods |= Abs ? SISrcMods::ABS : 0u;
+    Mods ^= Neg ? SISrcMods::NEG : 0u;
   } else if (Sext) {
     Mods |= SISrcMods::SEXT;
   }