ALSA: line6: remove line6_set_raw declaration

line6_set_raw has been removed since
commit 9f673d7a ("staging: line6: drop CONFIG_LINE6_USB_RAW"),
so remove it.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lore.kernel.org/r/20220909035443.1065737-2-cuigaosheng1@huawei.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>