net: ieee802154: adf7242: Fix some potential buffer overflow in adf7242_stats_show()

strncat() usage in adf7242_debugfs_init() is wrong.
The size given to strncat() is the maximum number of bytes that can be
written, excluding the trailing NULL.

Here, the size that is passed, DNAME_INLINE_LEN, does not take into account
the size of "adf7242-" that is already in the array.

In order to fix it, use snprintf() instead.

Fixes: 7302b9d9

 ("ieee802154/adf7242: Driver for ADF7242 MAC IEEE802154")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>