[Sema][NFC] Remove Redundant Condition

Condition `TypeQuals` is checked both in an outer and in an inner `if`
statement in static function `ConvertDeclSpecToType()` in file
`SemaType.cpp`. This patch removes the redundant inner check.

The issue was found using `clang-tidy` check under review
`misc-redundant-condition`. See https://reviews.llvm.org/D81272.

Differential Revision: https://reviews.llvm.org/D82563