powerpc/msi: Fix section mismatch warning in msi_bitmap_alloc()

Building with CONFIG_DEBUG_SECTION_MISMATCH gives the following warning:

  The function .msi_bitmap_alloc() references
  the function __init .memblock_virt_alloc_try_nid().

Memory allocation in msi_bitmap_alloc() uses either slab allocator or
memblock boot time allocator depending on slab_is_available().

So the section mismatch warning is correct, but in practice there is no
bug so mark msi_bitmap_alloc() as __init_refok.
Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
[mpe: Flesh out change log a bit]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/msi_bitmap.c

@@ -112,7 +112,7 @@ int msi_bitmap_reserve_dt_hwirqs(struct msi_bitmap *bmp)
 	return 0;
 }
 
-int msi_bitmap_alloc(struct msi_bitmap *bmp, unsigned int irq_count,
+int __init_refok msi_bitmap_alloc(struct msi_bitmap *bmp, unsigned int irq_count,
 		     struct device_node *of_node)
 {
 	int size;