swiotlb: mark swiotlb_memblock_alloc() as __init

swiotlb_memblock_alloc() calls memblock_alloc(), which calls
(__init) memblock_alloc_try_nid(). However, swiotlb_membloc_alloc()
can be marked as __init since it is only called by swiotlb_init_remap(),
which is already marked as __init. This prevents a modpost build
warning/error:

WARNING: modpost: vmlinux.o: section mismatch in reference: swiotlb_memblock_alloc (section: .text) -> memblock_alloc_try_nid (section: .init.text)
WARNING: modpost: vmlinux.o: section mismatch in reference: swiotlb_memblock_alloc (section: .text) -> memblock_alloc_try_nid (section: .init.text)

This fixes the build warning/error seen on ARM64, PPC64, S390, i386,
and x86_64.

Fixes: 8d58aa48 ("swiotlb: reduce the swiotlb buffer size on allocation failure")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Alexey Kardashevskiy <aik@amd.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux.dev
Cc: Mike Rapoport <rppt@kernel.org>
Cc: linux-mm@kvack.org
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/swiotlb.c

@@ -292,7 +292,8 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
 	return;
 }
 
-static void *swiotlb_memblock_alloc(unsigned long nslabs, unsigned int flags,
+static void __init *swiotlb_memblock_alloc(unsigned long nslabs,
+		unsigned int flags,
 		int (*remap)(void *tlb, unsigned long nslabs))
 {
 	size_t bytes = PAGE_ALIGN(nslabs << IO_TLB_SHIFT);