pinctrl: stmfx: Fix pin configuration issue

pinctrl: stmfx: Fix pin configuration issue

pin-controller pin's name must be equal to pin's name used in device
tree with "pins" DT property.

Issue detected on stm32mp157c-ev1 board with goodix touchscreen.
In DT, the goodix's pin is declared in DT with the node:

        goodix_pins: goodix {
		pins = "gpio14";
		bias-pull-down;
	};

Whereas in stmfx pin-controller driver, pin's name are equal to
"stmfx_gpioxx" where xx is the pin number.
This lead to not configure stmfx's pins at probe because pins is
identified by its name (see pinctrl_pin_name_to_selector() in
pinctrl-generic.c) and stmfx pin "gpio14" can't be found.

To fix this issue, come back to the original stmfx pin's name.

Revert "pinctrl: stmfx: update pin name"

This reverts commit 38d30cdcd65c73eeefac5efa328ad444a53b77dd.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Tested-by: Patrick DELAUNAY <patrick.delaunay@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>