[SCSI] megaraid: fix compiler warnings

The user ioctl mailbox can only support a 32 bit address for the
commands structure.  This is fine, since the area it's pointing to is
allocated with pci_alloc_consistent(), so it should be physically <
4GB.  Thus kill the ptr to u32 conversion warnings on 64 bit.

Signed-off-by: Martin J. Bligh <mbligh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: "Patro, Sumant" <Sumant.Patro@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>