ACPI: add dump_stack() to trace acpi_format_exception programming errors

Dump the stack so we can find the secretive caller to acpi_format_exception().

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/utilities/utglobal.c b/drivers/acpi/utilities/utglobal.c
index 1621655..93ea829 100644
--- a/drivers/acpi/utilities/utglobal.c
+++ b/drivers/acpi/utilities/utglobal.c
@@ -126,6 +126,7 @@
 			    "Unknown exception code: 0x%8.8X", status));
 
 		exception = "UNKNOWN_STATUS_CODE";
+		dump_stack();
 	}
 
 	return (ACPI_CAST_PTR(const char, exception));