altera-stapl: Use swap() instead of open coding it

Clean the following coccicheck warning:

./drivers/misc/altera-stapl/altera.c:955:51-52: WARNING opportunity for
swap().

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220505081539.91575-1-jiapeng.chong@linux.alibaba.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>