SELinux: security_read_policy should take a size_t not ssize_t

The len should be an size_t but is a ssize_t. Easy enough fix to silence
build warnings. We have no need for signed-ness.

Signed-off-by: Eric Paris <[e-mail]>
Reviewed-by: James Morris <[e-mail]>

security/selinux/include/security.h

···
 int security_mls_enabled(void);
 
 int security_load_policy(void *data, size_t len);
-int security_read_policy(void **data, ssize_t *len);
+int security_read_policy(void **data, size_t *len);
 size_t security_policydb_len(void);
 
 int security_policycap_supported(unsigned int req_cap);

security/selinux/ss/services.c

···
  * @len: length of data in bytes
  *
  */
-int security_read_policy(void **data, ssize_t *len)
+int security_read_policy(void **data, size_t *len)
 {
 	int rc;
 	struct policy_file fp;