[Hexagon][NFC] Remove redundant condition

Condition `secondReg` is checked both in an outer and in an inner `if`
statement in static function `canCompareBeNewValueJump()` in file
`HexagonNewValueJump.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/D82556