xen/acpi: off by one in read_acpi_id()

If acpi_id is == nr_acpi_bits, then we access one element beyond the end
of the acpi_psd[] array or we set one bit beyond the end of the bit map
when we do __set_bit(acpi_id, acpi_id_present);

Fixes: 59a56802 ("xen/acpi-processor: C and P-state driver that uploads said data to hypervisor.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/xen-acpi-processor.c

@@ -364,9 +364,9 @@ read_acpi_id(acpi_handle handle, u32 lvl, void *context, void **rv)
 	}
 	/* There are more ACPI Processor objects than in x2APIC or MADT.
 	 * This can happen with incorrect ACPI SSDT declerations. */
-	if (acpi_id > nr_acpi_bits) {
-		pr_debug("We only have %u, trying to set %u\n",
-			 nr_acpi_bits, acpi_id);
+	if (acpi_id >= nr_acpi_bits) {
+		pr_debug("max acpi id %u, trying to set %u\n",
+			 nr_acpi_bits - 1, acpi_id);
 		return AE_OK;
 	}
 	/* OK, There is a ACPI Processor object */