[ALSA] bt87X: fix freeing of shared interrupt

Call free_irq() after iounmap() because other devices could trigger our
shared interrupt handler.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>