net: dsa: bcm_sf2_cfp: fix an incorrect NULL check on list iterator

net: dsa: bcm_sf2_cfp: fix an incorrect NULL check on list iterator

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit 6da69b1da130e7d96766042750cd9f902e890eba ]

The bug is here:
	return rule;

The list iterator value 'rule' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty or no element
is found.

To fix the bug, return 'rule' when found, otherwise return NULL.

Fixes: ae7a5aff783c7 ("net: dsa: bcm_sf2: Keep copy of inserted rules")
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Link: https://lore.kernel.org/r/20220328032431.22538-1-xiam0nd.tong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit fd3f70b90772fe7a591e5290df1439a5313a9983)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>