ext4: Allow reading files with non-zero offset, clamp read len

Support was already implemented, but not hooked up. This fixes several
fails in the test cases.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
diff --git a/include/ext4fs.h b/include/ext4fs.h
index 965cd9e..bb55639 100644
--- a/include/ext4fs.h
+++ b/include/ext4fs.h
@@ -135,7 +135,7 @@
 
 struct ext_filesystem *get_fs(void);
 int ext4fs_open(const char *filename, loff_t *len);
-int ext4fs_read(char *buf, loff_t len, loff_t *actread);
+int ext4fs_read(char *buf, loff_t offset, loff_t len, loff_t *actread);
 int ext4fs_mount(unsigned part_length);
 void ext4fs_close(void);
 void ext4fs_reinit_global(void);