KVM: MTRR: simplify kvm_mtrr_get_guest_memory_type

kvm_mtrr_get_guest_memory_type never returns -1 which is implied
in the current code since if @type = -1 (means no MTRR contains the
range), iter.partial_map must be true

Simplify the code to indicate this fact

Signed-off-by: Xiao Guangrong <[e-mail]>
Tested-by: Alex Williamson <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/x86/kvm/mtrr.c

···
 	if (iter.mtrr_disabled)
 		return mtrr_disabled_type();
 
-	/* It is not covered by MTRRs. */
-	if (iter.partial_map) {
-		/*
-		 * We just check one page, partially covered by MTRRs is
-		 * impossible.
-		 */
-		WARN_ON(type != -1);
-		type = mtrr_default_type(mtrr_state);
-	}
+	/*
+	 * We just check one page, partially covered by MTRRs is
+	 * impossible.
+	 */
+	WARN_ON(iter.partial_map);
+
+	/* not contained in any MTRRs. */
+	if (type == -1)
+		return mtrr_default_type(mtrr_state);
+
 	return type;
 }
 EXPORT_SYMBOL_GPL(kvm_mtrr_get_guest_memory_type);