[clang] Fix -Wparentheses warning [NFC]
Without this gcc warns like
../../clang/lib/AST/ExprConstant.cpp:4091:63: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
4091 | (SrcVal.isVector() && SrcVal.getVectorLength() == 1) &&
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
4092 | "Not a valid HLSLAggregateSplatCast.");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
