ppc/spapr: H_ENTER_NESTED should restore host XER ca field

Fix missing env->ca restore when going from L2 back to the host.

Fixes: 120f738 ("spapr: implement nested-hv capability for the virtual hypervisor")
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

hw/ppc/spapr_hcall.c

@@ -1773,6 +1773,7 @@ void spapr_exit_nested(PowerPCCPU *cpu, int excp)
     env->cfar = spapr_cpu->nested_host_state->cfar;
     env->xer = spapr_cpu->nested_host_state->xer;
     env->so = spapr_cpu->nested_host_state->so;
+    env->ca = spapr_cpu->nested_host_state->ca;
     env->ov = spapr_cpu->nested_host_state->ov;
     env->ov32 = spapr_cpu->nested_host_state->ov32;
     env->ca32 = spapr_cpu->nested_host_state->ca32;