sched: fix warning in fs/proc/base.c

Stephen Rothwell reported this new (harmless) build warning on platforms that
define u64 to long:

 fs/proc/base.c: In function 'proc_pid_schedstat':
 fs/proc/base.c:352: warning: format '%llu' expects type 'long long unsigned int', but argument 3 has type 'u64'

asm-generic/int-l64.h platforms strike again: that file should be eliminated.

Fix it by casting the parameters to long long.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>