cpupower: Remove redundant error check

Remove double checks, and move the call to print_error to the
first check. Replace break by return, and return 0 on success.
The simplified version of the coccinelle semantic patch that
fixes this issue is as follows:

// <smpl>
@@
expression E; identifier pr; expression list es;
@@
for(...;...;...){
...
-	if (E) break;
+	if (E){
+		pr(es);
+		break;
+	}
...
}
- if(E) pr(es);
// </smpl>

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>