i2c: Constify i2c_algorithm declarations, part 1

Make struct i2c_algorithm declarations const in all i2c algorithm
drivers.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>