tools/power turbostat: Fix bogus SysWatt for forked program

Similar to delta_cpu(), delta_platform() is called in turbostat main
loop. This ensures accurate SysWatt readings in periodic monitoring mode
$ sudo turbostat -S -q --show power -i 1
CoreTmp PkgTmp PkgWatt CorWatt GFXWatt RAMWatt PKG_% RAM_% SysWatt
60 61 6.21 1.13 0.16 0.00 0.00 0.00 13.07
58 61 6.00 1.07 0.18 0.00 0.00 0.00 12.75
58 61 5.74 1.05 0.17 0.00 0.00 0.00 12.22
58 60 6.27 1.11 0.24 0.00 0.00 0.00 13.55

However, delta_platform() is missing for forked program and causes bogus
SysWatt reporting,
$ sudo turbostat -S -q --show power sleep 1
1.004736 sec
CoreTmp PkgTmp PkgWatt CorWatt GFXWatt RAMWatt PKG_% RAM_% SysWatt
57 58 6.05 1.02 0.16 0.00 0.00 0.00 0.03

Add missing delta_platform() for forked program.

Fixes: e5f687b89bc2 ("tools/power turbostat: Add RAPL psys as a built-in counter")
Signed-off-by: Zhang Rui <[e-mail]>
Signed-off-by: Len Brown <[e-mail]>

tools/power/x86/turbostat/turbostat.c

···
 	timersub(&tv_odd, &tv_even, &tv_delta);
 	if (for_all_cpus_2(delta_cpu, ODD_COUNTERS, EVEN_COUNTERS))
 		fprintf(outf, "%s: Counter reset detected\n", progname);
+	delta_platform(&platform_counters_odd, &platform_counters_even);
 
 	compute_average(EVEN_COUNTERS);
 	format_all_counters(EVEN_COUNTERS);