busybox

free: include SReclaimable in cached value

I noticed that the 'used' values from busybox free and
procps-ng free differed so I looked into why. It turns
out that procps-ng uses the "SReclaimable" value as
part of the cached value.

This was changed in
procps-ng commit 05d751c4f076a2f0118b914c5e51cfbb4762ad8e

function                                             old     new   delta
free_main                                            633     653     +20

Signed-off-by: Lukas Rusak <lorusak@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>