gpio: lp3943: remove unneeded platform_set_drvdata() call

This function call was found to be unnecessary as there is no equivalent
platform_get_drvdata() call, to access the private data of the driver.
Also, the private data is defined in this driver, so there is no risk of
it being accessed outside of this driver file.

Reviewed-by: Alexandru Ardelean <alex@shruggie.ro>
Signed-off-by: Andrei Coardos <aboutphysycs@gmail.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>