[POWERPC] Fix non-smp build

This fixes a compile error that only surfaces on CONFIG_SMP=n builds;
<asm/hvcall.h> seems to get pulled in through another header file for
SMP builds.  This problem was introduced by the hvcall stats patch.
Signed-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/kernel/asm-offsets.c

@@ -43,6 +43,7 @@
 #include <asm/cache.h>
 #include <asm/compat.h>
 #include <asm/mmu.h>
+#include <asm/hvcall.h>
 #endif
 
 #define DEFINE(sym, val) \