mpssd: fix buffer overflow warning

The compilation emits a warning in function ‘snprintf’,
    inlined from ‘set_cmdline’ at
    ../Documentation/mic/mpssd/mpssd.c:1541:9:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:64:10:
    warning: call to __builtin___snprintf_chk will always overflow
    destination buffer

This was introduced in commit f4a66c20

 ("misc: mic: Update MIC host
daemon with COSM changes") and is fixed by reverting the changes to the
size argument of these snprintf statements.

Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Mike Danese <mikedanese@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>