pmdadenki: remove unreachable code relating to sign (covscan)

Coverity static code checking noticed that there's a check for
negative power_now values in the denki PMDA - this cannot ever
happen, however, because an unsigned integer type is used when
reading and exporting this value.  As a result its safe to not
perform this additional check (current code is unreachable).

src/pmdas/denki/denki.c

@@ -317,10 +317,6 @@ static int read_batteries(void) {
 				pmNotifyErr(LOG_DEBUG, "Could not read %s.",filename);
 		fclose(fff);
 
-		// correct power_now, if we got a negative value
-		if ( power_now[bat]<0 )
-			power_now[bat]*=-1.0;
-
 		// capacity
 		pmsprintf(filename,sizeof(filename),"%s/capacity",battery_basepath[bat]);
 		fff=fopen(filename,"r");