Squelch potential buffer overflow warning

GCC 7.3 points out that a buffer of size PATH_MAX is being written to
with data that can theoretically overflow (a string of maximum size
PATH_MAX plus other constant-size strings).  Fix this by replacing
sprintf with snprintf.

Signed-off-by: astian <astian@elude.in>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>