fs/splice.c: fix mapping_gfp_mask usage

mapping_gfp_mask() is not supposed to store allocation contex details,
only page location details. So mapping_gfp_mask should be applied to the
pagecache page allocation, wheras normal (kernel mapped) memory should be
used for surrounding allocations such as radix-tree nodes allocated by
add_to_page_cache. Context modifiers should be applied on a per-callsite
basis.

So change splice to follow this convention (which is followed in similar
code patterns in core code).

Signed-off-by: Nick Piggin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

fs/splice.c

···
 				break;
 
 			error = add_to_page_cache_lru(page, mapping, index,
-						mapping_gfp_mask(mapping));
+						GFP_KERNEL);
 			if (unlikely(error)) {
 				page_cache_release(page);
 				if (error == -EEXIST)