rbd: Use min_t() to fix comparison of distinct pointer types warning

drivers/block/rbd.c: In function ‘zero_pages’:
drivers/block/rbd.c:1102: warning: comparison of distinct pointer types lacks a cast

Remove the hackish casts and use min_t() to fix this.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Alex Elder <elder@inktank.com>

drivers/block/rbd.c

@@ -1153,8 +1153,8 @@ static void zero_pages(struct page **pages, u64 offset, u64 end)
 		unsigned long flags;
 		void *kaddr;
 
-		page_offset = (size_t)(offset & ~PAGE_MASK);
-		length = min(PAGE_SIZE - page_offset, (size_t)(end - offset));
+		page_offset = offset & ~PAGE_MASK;
+		length = min_t(size_t, PAGE_SIZE - page_offset, end - offset);
 		local_irq_save(flags);
 		kaddr = kmap_atomic(*page);
 		memset(kaddr + page_offset, 0, length);