cputime: Bring cputime -> nsecs conversion

We already have nsecs_to_cputime(). Now we need to be able to convert
the other way around in order to fix a bug on steal time accounting.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

include/asm-generic/cputime_nsecs.h

@@ -44,6 +44,8 @@ typedef u64 __nocast cputime64_t;
 /*
  * Convert cputime <-> nanoseconds
  */
+#define cputime_to_nsecs(__ct)		\
+	(__force u64)(__ct)
 #define nsecs_to_cputime(__nsecs)	\
 	(__force cputime_t)(__nsecs)