fs/buffer.c: make __getblk_slow() static

__getblk_slow() was exported to modules in commit 3b5e6454aaf6
("fs/buffer.c: support buffer cache allocations with gfp modifiers").
This seems to have been a mistake, as no users were introduced nor was
the function declared in a header.  Change it back to 'static'.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/buffer.c

@@ -1078,7 +1078,7 @@ grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
 	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
 }
 
-struct buffer_head *
+static struct buffer_head *
 __getblk_slow(struct block_device *bdev, sector_t block,
 	     unsigned size, gfp_t gfp)
 {
@@ -1109,7 +1109,6 @@ __getblk_slow(struct block_device *bdev, sector_t block,
 			free_more_memory();
 	}
 }
-EXPORT_SYMBOL(__getblk_slow);
 
 /*
  * The relationship between dirty buffers and dirty pages: