powerpc/boot: Fix CONFIG_PPC_MPC52XX references

Commit 866bfc75f4 ("powerpc: conditionally compile platform-specific
serial drivers") made some code depend on CONFIG_PPC_MPC52XX, which
doesn't exist.

Fix it to use CONFIG_PPC_MPC52xx.

Fixes: 866bfc75f4 ("powerpc: conditionally compile platform-specific serial drivers")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200724131728.1643966-7-mpe@ellerman.id.au

arch/powerpc/boot/Makefile

@@ -117,7 +117,7 @@ src-wlib-y := string.S crt0.S stdio.c decompress.c main.c \
 		elf_util.c $(zlib-y) devtree.c stdlib.c \
 		oflib.c ofconsole.c cuboot.c
 
-src-wlib-$(CONFIG_PPC_MPC52XX) += mpc52xx-psc.c
+src-wlib-$(CONFIG_PPC_MPC52xx) += mpc52xx-psc.c
 src-wlib-$(CONFIG_PPC64_BOOT_WRAPPER) += opal-calls.S opal.c
 ifndef CONFIG_PPC64_BOOT_WRAPPER
 src-wlib-y += crtsavres.S

arch/powerpc/boot/serial.c

@@ -128,7 +128,7 @@ int serial_console_init(void)
 	         dt_is_compatible(devp, "fsl,cpm2-smc-uart"))
 		rc = cpm_console_init(devp, &serial_cd);
 #endif
-#ifdef CONFIG_PPC_MPC52XX
+#ifdef CONFIG_PPC_MPC52xx
 	else if (dt_is_compatible(devp, "fsl,mpc5200-psc-uart"))
 		rc = mpc5200_psc_console_init(devp, &serial_cd);
 #endif