powerpc/kvm/booke: Fix build break due to stack frame size warning

Commit ce11e48b7fdd256ec68b932a89b397a790566031 ("KVM: PPC: E500: Add
userspace debug stub support") added "struct thread_struct" to the
stack of kvmppc_vcpu_run().  thread_struct is 1152 bytes on my build,
compared to 48 bytes for the recently-introduced "struct debug_reg".
Use the latter instead.

This fixes the following error:

cc1: warnings being treated as errors
arch/powerpc/kvm/booke.c: In function 'kvmppc_vcpu_run':
arch/powerpc/kvm/booke.c:760:1: error: the frame size of 1424 bytes is larger than 1024 bytes
make[2]: *** [arch/powerpc/kvm/booke.o] Error 1
make[1]: *** [arch/powerpc/kvm] Error 2
make[1]: *** Waiting for unfinished jobs....

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 53e65a2..0591e05 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -681,7 +681,7 @@
 int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 {
 	int ret, s;
-	struct thread_struct thread;
+	struct debug_reg debug;
 #ifdef CONFIG_PPC_FPU
 	struct thread_fp_state fp;
 	int fpexc_mode;
@@ -723,9 +723,9 @@
 #endif
 
 	/* Switch to guest debug context */
-	thread.debug = vcpu->arch.shadow_dbg_reg;
-	switch_booke_debug_regs(&thread);
-	thread.debug = current->thread.debug;
+	debug = vcpu->arch.shadow_dbg_reg;
+	switch_booke_debug_regs(&debug);
+	debug = current->thread.debug;
 	current->thread.debug = vcpu->arch.shadow_dbg_reg;
 
 	kvmppc_fix_ee_before_entry();
@@ -736,8 +736,8 @@
 	   We also get here with interrupts enabled. */
 
 	/* Switch back to user space debug context */
-	switch_booke_debug_regs(&thread);
-	current->thread.debug = thread.debug;
+	switch_booke_debug_regs(&debug);
+	current->thread.debug = debug;
 
 #ifdef CONFIG_PPC_FPU
 	kvmppc_save_guest_fp(vcpu);