security: make args to virSecuritySELinuxContextAddRange() const

Neither of these are modified anywhere in the function, and the
function will soon be called with an arg that actually is a const.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

src/security/security_selinux.c

@@ -523,8 +523,8 @@ virSecuritySELinuxMCSGetProcessRange(char **sens,
 }
 
 static char *
-virSecuritySELinuxContextAddRange(char *src,
-                                  char *dst)
+virSecuritySELinuxContextAddRange(const char *src,
+                                  const char *dst)
 {
     const char *str = NULL;
     char *ret = NULL;