spi: fsl-spi: fix devm_ioremap_resource() error case

devm_ioremap_resource() doesn't return NULL but an ERR_PTR on error.
Reported-by: Jonas Gorsky <jogo@openwrt.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-cpm.c

@@ -310,10 +310,15 @@ int fsl_spi_cpm_init(struct mpc8xxx_spi *mspi)
 
 	if (mspi->flags & SPI_CPM1) {
 		struct resource *res;
+		void *pram;
 
 		res = platform_get_resource(to_platform_device(dev),
 					    IORESOURCE_MEM, 1);
-		mspi->pram = devm_ioremap_resource(dev, res);
+		pram = devm_ioremap_resource(dev, res);
+		if (IS_ERR(pram))
+			mspi->pram = NULL;
+		else
+			mspi->pram = pram;
 	} else {
 		unsigned long pram_ofs = fsl_spi_cpm_get_pram(mspi);