KVM: emulate: put pointers in the fetch_cache

This simplifies the code a bit, especially the overflow checks.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index fcf58cd..eb18117 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -242,8 +242,8 @@
 
 struct fetch_cache {
 	u8 data[15];
-	unsigned long start;
-	unsigned long end;
+	u8 *ptr;
+	u8 *end;
 };
 
 struct read_cache {