msm: sps: Use iomem attribute for base address

Clients may use ioremap api to obtain the bam base address.
Add iomem attribute to the base address field
in the public SPS structure to avoid type casts.

Change-Id: Iba2ec1a9d84c3d57e2ce314ba9dc0b81644db2fb
Signed-off-by: Ajay Prathi <aprathi@codeaurora.org>