Revert "gpu: nvgpu: cache gpu clk rate"

This reverts commit e9a6d179a4 ("gpu: nvgpu: cache gpu clk rate")

 - Real clock rate doesn't always equal clock rate requested by caller
 - call of clk_set_rate() and update of cached_rate are not atomic
 - Real root cause for Bug 2051688 is in bpmp and gboost design


Bug 2538692

Change-Id: I9248e0c69e2271ed2d0070587db59afa6f8160f2
Signed-off-by: Peng Liu <pengliu@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2109708
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/os/linux/platform_gk20a.h

@@ -300,9 +300,6 @@ struct gk20a_platform {
 	/* stream id to use */
 	u32 ltc_streamid;
 
-	/* scaling rate */
-	unsigned long cached_rate;
-
 	/* synchronized access to platform->clk_get_freqs */
 	struct nvgpu_mutex clk_get_freq_lock;
 };