selinux: fix avc audit messages

commit a2c51383 ("selinux: inline some AVC functions used only once")
introduced usage of audit_log_string() in place of audit_log_format()
for fixed strings.  However, audit_log_string() quotes the string.
This breaks the avc audit message format and userspace audit parsers.
Switch back to using audit_log_format().

Fixes: a2c51383 ("selinux: inline some AVC functions used only once")
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>