i2c: omap: constify dev_pm_ops structures

Declare dev_pm_ops structures as const as they are only stored in the pm
field of a device_driver structure. This field is of type const, so
dev_pm_ops structures having similar properties can be declared const
too.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>