net/ieee802154: drop unneeded assignment in llsec_iter_devkeys()

net/ieee802154: drop unneeded assignment in llsec_iter_devkeys()

In order to keep the code style consistency of the whole file,
redundant return value ‘rc’ and its assignments should be deleted

The clang_analyzer complains as follows:
net/ieee802154/nl-mac.c:1203:12: warning: Although the value stored to
'rc' is used in the enclosing expression, the value is never actually
read from 'rc'

No functional change, only more efficient.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/1619346299-40237-1-git-send-email-yang.lee@linux.alibaba.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>