staging: exfat: fix indentation issue

There is a declaration that requires indentation. Add in
the missing tab.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20191113164210.103586-1-colin.king@canonical.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>