fix compilation warning via PRI prefix

fix compilation warning via PRI prefix

modules/alsa/alsa-mixer.c:3110:21:
    warning: format '%lx' expects argument of type 'long unsigned int', but argument 7 has type 'pa_channel_position_mask_t' [-Wformat]
modules/alsa/alsa-mixer.c:3110:21:
    warning: format '%lx' expects argument of type 'long unsigned int', but argument 8 has type 'pa_channel_position_mask_t' [-Wformat]

pa_channel_position_mask_t is type defined to uint64_t, and to display
uint64_t, it's better to use PRIx64 primitives.

Signed-off-by: Deng Zhenrong <dzrongg@gmail.com>