xfs: rename the next_agno perag iteration variable

xfs: rename the next_agno perag iteration variable

[ Upstream commit f1788b5e5ee25bedf00bb4d25f82b93820d61189 ]

Rename the next_agno variable to be consistent across the several
iteration macros and shorten line length.

[backport: dependency for 8ed004eb9d07a5d6114db3e97a166707c186262d]

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>