fix build error on old compiler

  * vget_lane_** accepts constant value, not variable

modules/core/include/opencv2/core/hal/intrin_neon.hpp

@@ -285,8 +285,6 @@ template <typename T> static inline float16x4_t vld1_f16(const T* ptr)
 { return vreinterpret_f16_s16(vld1_s16((const short*)ptr)); }
 template <typename T> static inline void vst1_f16(T* ptr, float16x4_t a)
 { vst1_s16((short*)ptr, vreinterpret_s16_f16(a)); }
-static inline short vget_lane_f16(float16x4_t a, int b)
-{ return vget_lane_s16(vreinterpret_s16_f16(a), b); }
 
 struct v_float16x4
 {
@@ -302,7 +300,7 @@ struct v_float16x4
     }
     short get0() const
     {
-        return vget_lane_f16(val, 0);
+        return vget_lane_s16(vreinterpret_f16_s16(val), 0);
     }
     float16x4_t val;
 };