NTB: ntb_tool: reading the link file should not end in a NULL byte

When running ntb_test this warning is issued:

./ntb_test.sh: line 200: warning: command substitution: ignored null
byte in input

This is caused by the kernel returning one more byte than is necessary
when reading the link file.

Reduce the number of bytes read back to 2 as it was before the
commit that regressed this.

Fixes: 7f46c8b3 ("NTB: ntb_tool: Add full multi-port NTB API support")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Allen Hubbe <allenbh@gmail.com>
Tested-by: Alexander Fomichev <fomichev.ru@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_tool.c

@@ -504,7 +504,7 @@ static ssize_t tool_peer_link_read(struct file *filep, char __user *ubuf,
 	buf[1] = '\n';
 	buf[2] = '\0';
 
-	return simple_read_from_buffer(ubuf, size, offp, buf, 3);
+	return simple_read_from_buffer(ubuf, size, offp, buf, 2);
 }
 
 static TOOL_FOPS_RDWR(tool_peer_link_fops,
@@ -1690,4 +1690,3 @@ static void __exit tool_exit(void)
 	debugfs_remove_recursive(tool_dbgfs_topdir);
 }
 module_exit(tool_exit);
-