llist: avoid extra memory read in llist_add_batch

try_cmpxchg implicitly assigns old head->first value to "first" when
cmpxchg fails. There is no need to re-read the value in the loop.

Link: https://lkml.kernel.org/r/20221017145226.4044-1-ubizjak@gmail.com


Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>