mpu401 warning fixes

Fix these:

sound/oss/mpu401.c: In function 'attach_mpu401':
sound/oss/mpu401.c:1006: warning: cast to pointer from integer of different size
sound/oss/mpu401.c:1115: warning: cast to pointer from integer of different size
sound/oss/mpu401.c: In function 'unload_mpu401':
sound/oss/mpu401.c:1230: warning: cast to pointer from integer of different size

by making it implement the request_irq()/free_irq() cookies correctly.

Cc: Jaroslav Kysela <perex@suse.cz>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>