Make use of the swap macro instead of _manually_ swapping values
and remove unnecessary variable tmp.

This makes the code easier to read and maintain.

This code was detected with the help of Coccinelle.
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>