powerpc/mm: Fix build error in setup_initial_memory_limit

arch/powerpc/mm/tlb_nohash.c: In function 'setup_initial_memory_limit':
arch/powerpc/mm/tlb_nohash.c:588:29: error: 'ppc64_memblock_base' undeclared (first use in this function)
arch/powerpc/mm/tlb_nohash.c:588:29: note: each undeclared identifier is reported only once for each function it appears in

Due to a copy/paste typo with the following commit:

	commit cd3db0c4
	Author: Benjamin Herrenschmidt <benh@kernel.crashing.org>
	Date:   Tue Jul 6 15:39:02 2010 -0700

	    memblock: Remove rmo_size, burry it in arch/powerpc where it belongs
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/tlb_nohash.c

@@ -585,6 +585,6 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
 	ppc64_rma_size = min_t(u64, first_memblock_size, 0x40000000);
 
 	/* Finally limit subsequent allocations */
-	memblock_set_current_limit(ppc64_memblock_base + ppc64_rma_size);
+	memblock_set_current_limit(first_memblock_base + ppc64_rma_size);
 }
 #endif /* CONFIG_PPC64 */