audit: remove redundant initialization of static variables to 0

audit: remove redundant initialization of static variables to 0

Static variables are automatically initialized to 0 by the compiler.
Remove the redundant explicit assignments in kernel/audit.c to clean
up the code, align with standard kernel coding style, and fix the
following checkpatch.pl errors:

 ./scripts/checkpatch.pl kernel/audit.c | grep -A2 ERROR:
 ERROR: do not initialise statics to 0
 +	static unsigned long	last_check = 0;
 --
 ERROR: do not initialise statics to 0
 +	static int		messages   = 0;
 --
 ERROR: do not initialise statics to 0
 +	static unsigned long	last_msg = 0;

Signed-off-by: Ricardo Robaina <rrobaina@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>