xfs: fix error bailout in xfs_rtginode_create

smatch reported that we screwed up the error cleanup in this function.
Fix it.

Cc: <stable@vger.kernel.org> # v6.13-rc1
Fixes: ae897e0b ("xfs: support creating per-RTG files in growfs")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>