i2c: busses: make i2c_adapter const

Make these const as they are only used in a copy operation.
Done using Coccinelle.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>