Bluetooth: Mesh: Fix build warning with Warray-bounds

../zephyrNew/subsys/bluetooth/mesh/prov.c: In function
'bt_mesh_prov_reset_state': ../zephyrNew/subsys/bluetooth/mesh
/prov.c:61:2:warning: '__builtin_memset' offset [52, 292] from
the object at 'bt_mesh_prov_link' is out of the bounds of referenced
subobject 'dhkey' with type 'uint8_t[32]' {aka 'unsigned char[32]'}
at offset 19 [-Warray-bounds] 61 | memset(&bt_mesh_prov_link.dhkey, 0,

Fixes: #29634

Signed-off-by: Lingao Meng <mengabc1086@gmail.com>