perf tools: Fix possible (unlikely) buffer overflow

perf tools: Fix possible (unlikely) buffer overflow

cppcheck reported:
[tools/perf/util/sysfs.c:50]: (error) Width 4096 given in format string
(no. 1) is larger than destination buffer 'sysfs_mountpoint[4096]',
use %4095s to prevent overflowing it

-> All other places in the kernel that use STR(PATH_MAX)
   have a buffer size of PATH_MAX + 1.

Signed-off-by: Thomas Jarosch <thomas.jarosch@intra2net.com>
Link: http://lkml.kernel.org/r/50D9D30B.8090002@intra2net.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>