ALSA: usb-audio: sound: usb: usb true/false for bool return type

commit 1d4961d9

 upstream.

Use true/false for bool type return in uac_clock_source_is_valid().

Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Link: https://lore.kernel.org/r/20191029175200.GA7320@saurav
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>