rpmsgfs: fix nx_style

Signed-off-by: ligd <liguiding1@xiaomi.com>

fs/rpmsgfs/rpmsgfs_client.c

@@ -484,7 +484,7 @@ ssize_t rpmsgfs_client_read(FAR void *handle, int fd,
 
 out:
   nxsem_destroy(&cookie.sem);
-  return read.iov_len ? read.iov_len : ret;
+  return read.iov_len > 0 ? read.iov_len : ret;
 }
 
 ssize_t rpmsgfs_client_write(FAR void *handle, int fd,

fs/rpmsgfs/rpmsgfs_server.c

@@ -378,7 +378,7 @@ static int rpmsgfs_read_handler(FAR struct rpmsg_endpoint *ept,
   while (read < msg->count)
     {
       rsp = rpmsg_get_tx_payload_buffer(ept, &space, true);
-      if (!rsp)
+      if (rsp == NULL)
         {
           return -ENOMEM;
         }