s390/sysinfo: Replace sprintf() with snprintf() for buffer safety

s390/sysinfo: Replace sprintf() with snprintf() for buffer safety

Replace sprintf() with snprintf() when formatting symlink target name
to prevent potential buffer overflow. The link_to buffer is only 10
bytes, and using snprintf() ensures proper bounds checking if the
topology nesting limit value is unexpectedly large.

Signed-off-by: Josephine Pfeiffer <hi@josie.lol>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>