drivers/platform/x86/thinkpad_acpi.c: delete double assignment

Delete successive assignments to the same location.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression i;
@@

*i = ...;
 i = ...;
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -8497,7 +8497,6 @@ static void ibm_exit(struct ibm_struct *ibm)
 					   ibm->acpi->type,
 					   dispatch_acpi_notify);
 		ibm->flags.acpi_notify_installed = 0;
-		ibm->flags.acpi_notify_installed = 0;
 	}
 
 	if (ibm->flags.proc_created) {