powerpc: Fix prom_init on 32-bit OF machines

Commit e7943fbbfdb6eef03c003b374de1f802cc14f02a broke ppc32 using
Open Firmware client interface due to using the wrong relocation
macro when accessing the variable "linux_banner".

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 4d5ebb4..2e026c0 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -2283,7 +2283,7 @@
 	 */
 	prom_init_stdout();
 
-	prom_printf("Preparing to boot %s", PTRRELOC((char *)linux_banner));
+	prom_printf("Preparing to boot %s", RELOC(linux_banner));
 
 	/*
 	 * Get default machine type. At this point, we do not differentiate