target/arm: Fix float16 pairwise Neon ops on big-endian hosts

In the neon_padd/pmax/pmin helpers for float16, a cut-and-paste error
meant we were using the H4() address swizzler macro rather than the
H2() which is required for 2-byte data.  This had no effect on
little-endian hosts but meant we put the result data into the
destination Dreg in the wrong order on big-endian hosts.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20201028191712.4910-2-peter.maydell@linaro.org

target/arm/vec_helper.c

@@ -1858,10 +1858,10 @@ DO_ABA(gvec_uaba_d, uint64_t)
         r2 = float16_##OP(m[H2(0)], m[H2(1)], fpst);                    \
         r3 = float16_##OP(m[H2(2)], m[H2(3)], fpst);                    \
                                                                         \
-        d[H4(0)] = r0;                                                  \
-        d[H4(1)] = r1;                                                  \
-        d[H4(2)] = r2;                                                  \
-        d[H4(3)] = r3;                                                  \
+        d[H2(0)] = r0;                                                  \
+        d[H2(1)] = r1;                                                  \
+        d[H2(2)] = r2;                                                  \
+        d[H2(3)] = r3;                                                  \
     }
 
 DO_NEON_PAIRWISE(neon_padd, add)