zstd: add cast to some ZSTD_memcpy()

Visual Studio 2019 isn't liking the const disagreement for the
destination argument. We have warnings as errors enabled and this
leads to build failures. Adding an inline cast to remove the `const`
seems to make things happy.

I reported this upstream at
facebook/zstd#3515.

zstd/zstd.c

@@ -36243,7 +36243,7 @@ void HUF_decompress4X1_usingDTable_internal_fast_c_loop(HUF_DecompressFastArgs*
 
     /* Copy the arguments to local variables */
     ZSTD_memcpy(&bits, &args->bits, sizeof(bits));
-    ZSTD_memcpy(&ip, &args->ip, sizeof(ip));
+    ZSTD_memcpy((BYTE*)&ip, &args->ip, sizeof(ip));
     ZSTD_memcpy(&op, &args->op, sizeof(op));
 
     assert(MEM_isLittleEndian());
@@ -36326,7 +36326,7 @@ void HUF_decompress4X1_usingDTable_internal_fast_c_loop(HUF_DecompressFastArgs*
 
     /* Save the final values of each of the state variables back to args. */
     ZSTD_memcpy(&args->bits, &bits, sizeof(bits));
-    ZSTD_memcpy(&args->ip, &ip, sizeof(ip));
+    ZSTD_memcpy((BYTE*)&args->ip, &ip, sizeof(ip));
     ZSTD_memcpy(&args->op, &op, sizeof(op));
 }
 
@@ -37023,7 +37023,7 @@ void HUF_decompress4X2_usingDTable_internal_fast_c_loop(HUF_DecompressFastArgs*
 
     /* Copy the arguments to local registers. */
     ZSTD_memcpy(&bits, &args->bits, sizeof(bits));
-    ZSTD_memcpy(&ip, &args->ip, sizeof(ip));
+    ZSTD_memcpy((BYTE*)&ip, &args->ip, sizeof(ip));
     ZSTD_memcpy(&op, &args->op, sizeof(op));
 
     oend[0] = op[1];
@@ -37146,7 +37146,7 @@ void HUF_decompress4X2_usingDTable_internal_fast_c_loop(HUF_DecompressFastArgs*
 
     /* Save the final values of each of the state variables back to args. */
     ZSTD_memcpy(&args->bits, &bits, sizeof(bits));
-    ZSTD_memcpy(&args->ip, &ip, sizeof(ip));
+    ZSTD_memcpy((BYTE*)&args->ip, &ip, sizeof(ip));
     ZSTD_memcpy(&args->op, &op, sizeof(op));
 }