thunderbolt: debugfs: Fix uninitialized return in counters_write()

If the first line is in an invalid format then the "ret" value is
uninitialized.  We should return -EINVAL instead.

Fixes: 54e41810 ("thunderbolt: Add debugfs interface")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/debugfs.c

@@ -231,6 +231,7 @@ static ssize_t counters_write(struct file *file, const char __user *user_buf,
 		char *line = buf;
 		u32 val, offset;
 
+		ret = -EINVAL;
 		while (parse_line(&line, &offset, &val, 1, 4)) {
 			ret = tb_port_write(port, &val, TB_CFG_COUNTERS,
 					    offset, 1);