btrfs: don't use GFP_HIGHMEM for free-space-tree bitmap kzalloc

This was copied incorrectly from the __vmalloc call.

Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index dfa8124..81a053d 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -164,7 +164,7 @@
 	if  (bitmap_size <= PAGE_SIZE)
 		return kzalloc(bitmap_size, GFP_NOFS);
 
-	mem = kzalloc(bitmap_size, GFP_NOFS | __GFP_HIGHMEM | __GFP_NOWARN);
+	mem = kzalloc(bitmap_size, GFP_NOFS | __GFP_NOWARN);
 	if (mem)
 		return mem;