Existing blogic_msg() invocations do not appear to overrun its internal
buffer of a fixed length of 100, which would cause stack corruption, but
it's easy to miss with possible further updates and a fix is cheap in
performance terms, so limit the output produced into the buffer by using
vscnprintf() rather than vsprintf().

Link: https://lore.kernel.org/r/alpine.DEB.2.21.2104201939390.44318@angie.orcam.me.ukAcked-by: Khalid Aziz <khalid@gonehiking.org>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>