mpt2sas: annotate ioc->reply_post_host_index as __iomem

The MPT2SAS_ADAPTER reply_post_host_index[] holds calculated addresses
in memory mapped register space.  Add an "__iomem" annotation to silence
the following sparse warnings:

  drivers/scsi/mpt2sas/mpt2sas_base.c:1006:43:
    warning: incorrect type in argument 2 (different address spaces)
       expected void volatile [noderef] <asn:2>*addr
       got unsigned long long [usertype] *<noident>

  drivers/scsi/mpt2sas/mpt2sas_base.c:4299:22:
    warning: cast removes address space of expression
  drivers/scsi/mpt2sas/mpt2sas_base.c:4303:27:
    warning: cast removes address space of expression

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Sreekanth Reddy <Sreekanth.Reddy@avagotech.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>