xfs: avoid unnecessary open zone check in xfs_select_zone_nowait()

When xfs_select_zone_nowait() is called with pack_tight equal to true,
the function xfs_select_open_zone_mru() is called if no open zone is
returned by xfs_select_open_zone_lru(), that is, when oz is NULL. The
open zone pointer return of xfs_select_zone_nowait() is then checked,
but this check is outside of the "if (pack_tight)" that trigered the
call to xfs_select_open_zone_mru(). In other word, this check is
unnecessarily done even when pack_tight is false.

Move the check for the return value of the call to
xfs_select_open_zone_mru() inside the if that controls the call to this
function, so that we do not uselessly test again the value of oz when
pack_tight is false.

No functional changes.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Carlos Maiolino <cem@kernel.org>