[PATCH powerpc] Fix compiling error in rng.c

This patch tries to fix following compiling errors, by including the
needed header file:

arch/powerpc/platforms/pseries/rng.c: In function 'pseries_get_random_long':
arch/powerpc/platforms/pseries/rng.c:20: error: 'PLPAR_HCALL_BUFSIZE' undeclared (first use in this function)
...

Signed-off-by: Li Zhong <redacted>
---
 arch/powerpc/platforms/pseries/rng.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/rng.c b/arch/powerpc/platforms/pseries/rng.c
index a702f1c..62c7838 100644
--- a/arch/powerpc/platforms/pseries/rng.c
+++ b/arch/powerpc/platforms/pseries/rng.c

@@ -13,7 +13,7 @@
 #include <linux/of.h>
 #include <asm/archrandom.h>
 #include <asm/machdep.h>
-
+#include <asm/hvcall.h>
 
 static int pseries_get_random_long(unsigned long *v)
 {