drm/amd/pm: Replace one-element array with flexible-array in struct phm_phase_shedding_limits_table

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member in
struct phm_phase_shedding_limits_table, instead of a one-element array,
and use the struct_size() helper to calculate the size for the allocation.

Also, save some heap space as the original code is multiplying
ptable->ucNumEntries by sizeof(struct phm_phase_shedding_limits_table)
when it should have multiplied it by sizeof(struct phm_phase_shedding_limits_record)
instead.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arraysBuild-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/5f7c5d36.6PStUZp2HRxAz7IM%25lkp@intel.com/Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/inc/hwmgr.h

@@ -161,7 +161,7 @@ struct phm_vce_clock_voltage_dependency_record {
 
 struct phm_phase_shedding_limits_table {
 	uint32_t                           count;
-	struct phm_phase_shedding_limits_record  entries[1];
+	struct phm_phase_shedding_limits_record  entries[];
 };
 
 struct phm_vceclock_voltage_dependency_table {

drivers/gpu/drm/amd/pm/powerplay/hwmgr/processpptables.c

@@ -1530,16 +1530,12 @@ static int init_phase_shedding_table(struct pp_hwmgr *hwmgr,
 				(((unsigned long)powerplay_table4) +
 				le16_to_cpu(powerplay_table4->usVddcPhaseShedLimitsTableOffset));
 			struct phm_phase_shedding_limits_table *table;
-			unsigned long size, i;
+			unsigned long i;
 
 
-			size = sizeof(unsigned long) +
-				(sizeof(struct phm_phase_shedding_limits_table) *
-				ptable->ucNumEntries);
-
-			table = kzalloc(size, GFP_KERNEL);
-
-			if (table == NULL)
+			table = kzalloc(struct_size(table, entries, ptable->ucNumEntries),
+					GFP_KERNEL);
+			if (!table)
 				return -ENOMEM;
 
 			table->count = (unsigned long)ptable->ucNumEntries;