gpio: max77620: remove unneeded platform_set_drvdata() call

This function call is not required because no counterpart
platform_get_drvdata() call is present to leverage the private data of
the driver.
Since the private data is confined to this driver file, external access
is not feasible.
The use of this function appears redundant in the current context of the
driver's implementation.

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>