ext4: fix async i/o writes beyond 4GB to a sparse file

The "offset" member in ext4_io_end holds bytes, not blocks, so
ext4_lblk_t is wrong - and too small (u32).

This caused the async i/o writes to sparse files beyond 4GB to fail
when they wrapped around to 0.

Also fix up the type of arguments to ext4_convert_unwritten_extents(),
it gets ssize_t from ext4_end_aio_dio_nolock() and
ext4_ext_direct_IO().

Reported-by: Giel de Nijs <giel@vectorwise.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e119524..2059c34 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3551,7 +3551,7 @@
 {
 	struct inode *inode = io->inode;
 	loff_t offset = io->offset;
-	size_t size = io->size;
+	ssize_t size = io->size;
 	int ret = 0;
 
 	ext4_debug("end_aio_dio_onlock: io 0x%p from inode %lu,list->next 0x%p,"