I2C: i2c-omap: Change device name: i2c_omap -> omap_i2c

The convention for omap device naming is omap_XXX.

Rename the device and driver name in order to stick
to this naming convention.

Change device name in clock nodes as well.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Cc: Ben Dooks <ben-i2c@fluff.org>
Acked-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>