i2c: nomadik: constify amba_id

amba_id are not supposed to change at runtime. All functions
working with const amba_id. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>