gpio/omap: Remove bank->id information and misc cleanup

The driver does not need anymore any id to identify the GPIO instance.
Remove every occurence of the bank->id inside the driver.

Remove two trailing spaces.
Add a dev variable for better readability in probe.
Remove unused variable bank->pbase.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Acked-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>