gpu: nvgpu: avoid faulty elpg protection

Don't store the return value of elpg re-enable if disable fails; this
could make the local status value zero again, causing the elpg-protected
call to be executed with elpg still enabled and elpg re-enabled twice.

Commit c905858565 ("gpu: nvgpu: add cg and pg function") introduced
this bug; failure of re-enabling after a failed disable might be another
problem (and it's not clear why this is done in the first place) which
isn't propagated to the caller, but that would belong to another patch.

Bug 200565050

Change-Id: I7cf7a0887ae59e85bf0c56c38aaaadfefd16cc1c
Signed-off-by: Konsta Hölttä <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2541859
Reviewed-by: Debarshi Dutta <ddutta@nvidia.com>
Reviewed-by: svc_kernel_abi <svc_kernel_abi@nvidia.com>
Reviewed-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/include/nvgpu/power_features/pg.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2019-2021, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -34,7 +34,7 @@ struct gk20a;
 		int err = 0; \
 		err = nvgpu_pg_elpg_disable(g);\
 		if (err != 0) {\
-			err = nvgpu_pg_elpg_enable(g);\
+			(void)nvgpu_pg_elpg_enable(g);\
 		}\
 		if (err == 0) { \
 			err = (func); \