pinctrl: pinconf-generic: Fix memory leak in pinconf_generic_parse_dt_config()

pinctrl: pinconf-generic: Fix memory leak in pinconf_generic_parse_dt_config()

In pinconf_generic_parse_dt_config(), if parse_dt_cfg() fails, it returns
directly. This bypasses the cleanup logic and results in a memory leak of
the cfg buffer.

Fix this by jumping to the out label on failure, ensuring kfree(cfg) is
called before returning.

Fixes: 90a18c512884 ("pinctrl: pinconf-generic: Handle string values for generic properties")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Reviewed-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>