pinctrl: qcom: lpass-lpi: drop unused runtime-PM write helper

pinctrl: qcom: lpass-lpi: drop unused runtime-PM write helper

lpi_gpio_write() became unused after the PM clock runtime conversion
switched write paths to register helper calls inside callers that already
hold an active runtime-PM reference.

With -Werror this triggers:
  error: 'lpi_gpio_write' defined but not used [-Wunused-function]

Drop the dead wrapper and rename the low-level MMIO helpers from
__lpi_gpio_* to lpi_gpio_*_reg for neutral register-accessor naming.

Fixes: b719ede389d8 ("pinctrl: qcom: lpass-lpi: Switch to PM clock framework for runtime PM")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/all/f03850f6-186d-4988-a450-e6e95f24a551@kernel.org/
Signed-off-by: Ajay Kumar Nandam <ajay.nandam@oss.qualcomm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>