f2fs: clear PageError on the read path

When running fault injection test, I hit somewhat wrong behavior in f2fs_gc ->
gc_data_segment():

0. fault injection generated some PageError'ed pages

1. gc_data_segment
 -> f2fs_get_read_data_page(REQ_RAHEAD)

2. move_data_page
 -> f2fs_get_lock_data_page()
  -> f2f_get_read_data_page()
   -> f2fs_submit_page_read()
    -> submit_bio(READ)
  -> return EIO due to PageError
  -> fail to move data

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>