ARM: fix a section mismatch warning with our use of memblock

Commit 716a3dc2 (ARM: Add arm_memblock_steal() to allocate memory
away from the kernel) added a function which calls memblock_alloc().
This causes a section conflict:

WARNING: vmlinux.o(.text+0xc614): Section mismatch in reference from the function arm_memblock_steal() to the function .init.text:memblock_alloc()
The function arm_memblock_steal() references
the function __init memblock_alloc().
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/init.c

@@ -310,7 +310,7 @@ static void arm_memory_present(void)
 
 static bool arm_memblock_steal_permitted = true;
 
-phys_addr_t arm_memblock_steal(phys_addr_t size, phys_addr_t align)
+phys_addr_t __init arm_memblock_steal(phys_addr_t size, phys_addr_t align)
 {
 	phys_addr_t phys;