KVM: PPC: Book3S: Fix compile error in XICS emulation

Commit 8e44ddc3f3 ("powerpc/kvm/book3s: Add support for H_IPOLL and H_XIRR_X in XICS emulation") added a call to get_tb() but didn't include the header that defines it, and on some configs this means book3s_xics.c fails to compile:

arch/powerpc/kvm/book3s_xics.c: In function ‘kvmppc_xics_hcall’:
arch/powerpc/kvm/book3s_xics.c:812:3: error: implicit declaration of function ‘get_tb’ [-Werror=implicit-function-declaration]

---
 arch/powerpc/kvm/book3s_xics.c | 1 +
 1 file changed, 1 insertion(+)

index 94c1dd4..a3a5cb8 100644
@@ -19,6 +19,7 @@
 #include <asm/hvcall.h>
 #include <asm/xics.h>
 #include <asm/debug.h>
+#include <asm/time.h>
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>

1.8.3.1