fsx: add missing -T option to getopt_long()

fsx: add missing -T option to getopt_long()

Currently fsx fails with an invalid argument error when we pass the -T
option (do not use dontcache IO) to it because it's not listed in the
gepopt_long() call.

Fix this and add T to the getopt_long() call.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>