ALSA: bebob: Uninitialized id returned by saffirepro_both_clk_src_get

ALSA: bebob: Uninitialized id returned by saffirepro_both_clk_src_get

snd_bebob_stream_check_internal_clock() may get an id from
saffirepro_both_clk_src_get (via clk_src->get()) that was uninitialized.

a) make logic in saffirepro_both_clk_src_get explicit
b) test if id used in snd_bebob_stream_check_internal_clock matches array size

[fixed missing signed prefix to *_maps[] by tiwai]

Signed-off-by: Christian Vogel <[email protected]>
Reviewed-by: Takashi Sakamoto <[email protected]>
Cc: <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>