fix brd allocation flags

While looking at the implementation of the Ram backed block device
driver, I stumbled across a write-only local variable, which makes
little sense, so I assume it should actually work like this:

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/brd.c

@@ -108,7 +108,7 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
 #ifndef CONFIG_BLK_DEV_XIP
 	gfp_flags |= __GFP_HIGHMEM;
 #endif
-	page = alloc_page(GFP_NOIO | __GFP_HIGHMEM | __GFP_ZERO);
+	page = alloc_page(gfp_flags);
 	if (!page)
 		return NULL;