mtd: rawnand: lpc32xx_slc: Switch to using pm_ptr()

The switch to using the gpiod API removed the last user of
lpc32xx_wp_disable() outside #ifdef CONFIG_PM, causing build failures if
CONFIG_PM=n:

    drivers/mtd/nand/raw/lpc32xx_slc.c:318:13: error: ‘lpc32xx_wp_disable’ defined but not used [-Werror=unused-function]
      318 | static void lpc32xx_wp_disable(struct lpc32xx_nand_host *host)
          |             ^~~~~~~~~~~~~~~~~~

Fix this by switching from #ifdef CONFIG_PM to pm_ptr(), increasing
compile-coverage as a side-effect.

Reported-by:  <noreply@ellerman.id.au>
Fixes: 6b923db2 ("mtd: rawnand: lpc32xx_slc: switch to using gpiod API")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221027131028.3838303-2-geert@linux-m68k.org