ACPI: thinkpad-acpi: silence _sta warning

When both CONFIG_THINKPAD_ACPI_DOCK and CONFIG_THINKPAD_ACPI_BAY are
undefined, _sta is not used and that causes a gcc warning.  Fix it
(and I think this is a regression, I am pretty sure I fixed this once
before, sorry about that).

Issue reported by: Pritt Laes.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Pritt Laes <plaes@plaes.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/misc/thinkpad_acpi.c

@@ -414,6 +414,7 @@ static int acpi_ec_write(int i, u8 v)
 	return 1;
 }
 
+#if defined(CONFIG_THINKPAD_ACPI_DOCK) || defined(CONFIG_THINKPAD_ACPI_BAY)
 static int _sta(acpi_handle handle)
 {
 	int status;
@@ -423,6 +424,7 @@ static int _sta(acpi_handle handle)
 
 	return status;
 }
+#endif
 
 static int issue_thinkpad_cmos_command(int cmos_cmd)
 {