build: fix Wlog_Error_String overflow issues

build: fix Wlog_Error_String overflow issues

The 'Wlog_Error_String' string is defined to be 256 bytes in length,
but in two places we write into it with a format that contains a
string (wfile->w_file) that has length 1024.  This can overflow
Wlog_Error_String, as we see in the new compiler warnings from gcc
7.2.1:

 write_log.c:124:37: warning: ‘%s’ directive writing up to 1023 bytes into
 a region of size 224 [-Wformat-overflow=]
 "Could not open write_log - open(%s, %#o, %#o) failed:  %s\n",
  ^~

Fix this by increasing the length of Wlog_Error_String to 1280
characters (1024 for wfile->w_file plus 256 for the rest of the
format string), and by using snprintf() instead of sprintf() so we
are sure we don't overflow.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>