[PATCH] one more iomap s390 build fix

Commit 9ac7849e causes this on S390:

  drivers/built-in.o: In function `dmam_noncoherent_release':
    dma-mapping.c:(.text+0x1515c): undefined reference to `dma_free_noncoherent'
  drivers/built-in.o: In function `dmam_free_noncoherent':
    undefined reference to `dma_free_noncoherent'
  drivers/built-in.o: In function `dmam_alloc_noncoherent':
    undefined reference to `dma_alloc_noncoherent'
  make: *** [.tmp_vmlinux1] Error 1

Cc: Tejun Heo <htejun@gmail.com>
Acked-by: Jeff Garzik <jeff@garzik.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>