[X86] Refactor GetSSETypeAtOffset to fix pr51813

D105263 adds support for _Float16 type. It introduced a bug (pr51813) that generates a <4 x half> type instead the default double when passing blank structure by SSE registers.

Although I doubt it may expose a bug somewhere other than D105263, it's good to avoid return half type when no half type in arguments.

Reviewed By: LuoYuanke

Differential Revision: https://reviews.llvm.org/D109607