Simplify p9_fid_put cleanup path in many 9p functions since the function
is noop on null or error fids.
Also make the *_add_fid() helpers "steal" the fid by nulling its
pointer, so put after them will be noop.
This should lead to no change of behaviour
Link: https://lkml.kernel.org/r/20220612085330.1451496-7-asmadeus@codewreck.org
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
dafbe68973