tests/extmod/vfs_lfs_error: Use small ints in seek error test.

So accessing the seek offset (at the C level) doesn't cause an
OverflowError on 32-bit targets.

tests/extmod/vfs_lfs_error.py

@@ -106,8 +106,9 @@ def test(bdev, vfs_class):
 
     # error during seek
     with vfs.open('testfile', 'r') as f:
+        f.seek(1 << 30) # SEEK_SET
         try:
-            f.seek(1 << 31)
+            f.seek(1 << 30, 1) # SEEK_CUR
         except OSError:
             print('seek OSError')