i2c: pca-isa: Utilize the module_isa_driver macro

This driver does not do anything special in module init/exit. This patch
eliminates the module init/exit boilerplate code by utilizing the
module_isa_driver macro.

Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
[wsa: remove two empty lines while here]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>