Btrfs: Fix compile warnings on 32 bit machines

Simple casting here and there to fix things up.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index ba2527d..5b9f700 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -370,7 +370,7 @@
 
 	data_in = kmap(pages_in[page_in_index]);
 	workspace->inf_strm.next_in = data_in;
-	workspace->inf_strm.avail_in = min(srclen, PAGE_CACHE_SIZE);
+	workspace->inf_strm.avail_in = min_t(size_t, srclen, PAGE_CACHE_SIZE);
 	workspace->inf_strm.total_in = 0;
 
 	workspace->inf_strm.total_out = 0;