mei: debugfs: adjust active clients print buffer

In case of many active host clients clients (41 and more) 1K buffer
is not enough for full information print.
Calculate buffer size according to real clients number.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>