[WebAssembly] Fix lane index size for f16x8 extract_lane. (#108118)

Author: brendandahl

llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td

@@ -684,7 +684,7 @@ defm EXTRACT_LANE_F16x8 :
   HALF_PRECISION_I<(outs F32:$dst), (ins V128:$vec, vec_i8imm_op:$idx),
                    (outs), (ins vec_i8imm_op:$idx),
                    [(set (f32 F32:$dst), (int_wasm_extract_lane_f16x8
-                    (v8f16 V128:$vec), (i32 LaneIdx16:$idx)))],
+                    (v8f16 V128:$vec), (i32 LaneIdx8:$idx)))],
                    "f16x8.extract_lane\t$dst, $vec, $idx",
                    "f16x8.extract_lane\t$idx", 0x121>;