gpio: syscon: Remove usage of syscon_regmap_lookup_by_compatible

Since version 5.13, the standard syscon bindings have been added
to all clps711x DT nodes, so we can now use the more general
syscon_regmap_lookup_by_phandle function to get the syscon pointer.

This patch removes the usage of the syscon_regmap_lookup_by_compatible
function as it is no longer used in the driver.

Signed-off-by: Alexander Shiyan <eagle.alexander923@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>