[ALSA] echo3g_dsp.c shouldn't include #include <linux/irq.h>

Despite being under linux/, linux/irq.h shouldn't be #include'd by arch
independent code.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>