staging: slicoss: remove UPDATE_STATS_GB macro and inline code

This patch removes UPDATE_STATS_GB macro in slic.h header file
and just inline code. This improve readability.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>