riscv: Fix 32-bit RISC-V boot failure

Commit dd2d082 ("riscv: Cleanup setup_bootmem()") adjusted
the calling sequence in setup_bootmem(), which invalidates the fix
commit de043da ("RISC-V: Fix usage of memblock_enforce_memory_limit")
did for 32-bit RISC-V unfortunately.

So now 32-bit RISC-V does not boot again when testing booting kernel
on QEMU 'virt' with '-m 2G', which was exactly what the original
commit de043da ("RISC-V: Fix usage of memblock_enforce_memory_limit")
tried to fix.

Fixes: dd2d082 ("riscv: Cleanup setup_bootmem()")
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/mm/init.c

@@ -123,7 +123,7 @@ void __init setup_bootmem(void)
 {
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
 	phys_addr_t vmlinux_start = __pa_symbol(&_start);
-	phys_addr_t dram_end = memblock_end_of_DRAM();
+	phys_addr_t dram_end;
 	phys_addr_t max_mapped_addr = __pa(~(ulong)0);
 
 #ifdef CONFIG_XIP_KERNEL
@@ -146,6 +146,8 @@ void __init setup_bootmem(void)
 #endif
 	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
 
+	dram_end = memblock_end_of_DRAM();
+
 	/*
 	 * memblock allocator is not aware of the fact that last 4K bytes of
 	 * the addressable memory can not be mapped because of IS_ERR_VALUE