commit 05f54903 upstream.

For flexfiles driver, we might choose to read from mirror index other
than 0 while mirror_count is always 1 for read.
Reported-by: Jean Spector <jean@primarydata.com>
Cc: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>