Bluetooth: Mesh: fix shadow declare

CC:  mesh/adv.c
mesh/adv.c: In function 'bt_mesh_scan_cb':
mesh/adv.c:247:13: warning: declaration of 'adv_type'
                   shadows a global declaration [-Wshadow]
  247 |        u8_t adv_type, struct net_buf_simple *buf)
      |        ~~~~~^~~~~~~~
mesh/adv.c:58:19: note: shadowed declaration is here
   58 | static const u8_t adv_type[] = {
      |                   ^~~~~~~~

CC:  mesh/prov.c
mesh/prov.c: In function 'bt_mesh_prov_enable':
mesh/prov.c:1203:30: warning: declaration of 'prov'
                     shadows a global declaration [-Wshadow]
 1203 |   const struct bt_mesh_prov *prov = bt_mesh_prov_get();
      |                              ^~~~
mesh/prov.c:129:35: note: shadowed declaration is here
  129 | static const struct bt_mesh_prov *prov;
      |                                   ^~~~

Signed-off-by: chao an <anchao@xiaomi.com>