linux-user/syscall: Replace g_malloc0 + memcpy with g_memdup

No need to use g_malloc0 to zero the memory if we memcpy to
the whole buffer afterwards anyway. Actually, there is even
a function which combines both steps, g_memdup, so let's use
this function here instead.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

linux-user/syscall.c

@@ -5325,8 +5325,7 @@ static abi_long do_open_by_handle_at(abi_long mount_fd, abi_long handle,
         return -TARGET_EFAULT;
     }
 
-    fh = g_malloc0(total_size);
-    memcpy(fh, target_fh, total_size);
+    fh = g_memdup(target_fh, total_size);
     fh->handle_bytes = size;
     fh->handle_type = tswap32(target_fh->handle_type);