cpupower: mperf monitor: Correct use of ! and &

In commit ae91d60b, a bug was fixed that
involved converting !x & y to !(x & y).  The code below shows the same
pattern, and thus should perhaps be fixed in the same way.

The Coccinelle semantic patch that makes this change is as follows:

// <smpl>
@@ expression E1,E2; @@
(
  !E1 & !E2
|
- !E1 & E2
+ !(E1 & E2)
)
// </smpl>

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>