powerpc: Remove leftover cputime_to_nsecs call causing build error

This type conversion is a leftover that got ignored during the kcpustat
conversion to nanosecs, resulting in build breakage with config having
CONFIG_NO_HZ_FULL=y.

	arch/powerpc/kernel/time.c: In function 'running_clock':
	arch/powerpc/kernel/time.c:712:2: error: implicit declaration of function 'cputime_to_nsecs' [-Werror=implicit-function-declaration]
	  return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]);

All we need is to remove it.

Fixes: e7f340ca9c07 ("powerpc, sched/cputime: Remove unused cputime definitions")
Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/time.c

@@ -689,7 +689,7 @@ unsigned long long running_clock(void)
 	 * time and on a host which doesn't do any virtualisation TB *should* equal
 	 * VTB so it makes no difference anyway.
 	 */
-	return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]);
+	return local_clock() - kcpustat_this_cpu->cpustat[CPUTIME_STEAL];
 }
 #endif