[XFS] fix uninitialised variable bug in dquot release.

gcc is warning about an uninitialised variable in xfs_growfs_rt().
This is a false positive. Fix it by changing the scope of the
transaction pointer to wholly within the internal loop inside
the function.

While there, preemptively change xfs_growfs_rt_alloc() in the
same way as it has exactly the same structure as xfs_growfs_rt()
but gcc is not warning about it. Yet.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Niv Sardi <xaiki@sgi.com>