vm: convert snd_pcm_lib_mmap_iomem() to vm_iomap_memory() helper

commit 0fe09a45c4848b5b5607b968d959fdc1821c161d upstream.

This is my example conversion of a few existing mmap users.  The pcm
mmap case is one of the more straightforward ones.

Acked-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>