drm/amd/pm: Replace one-element array with flexible-array in struct phm_cac_leakage_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_cac_leakage_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
table->ucNumEntries by sizeof(struct phm_cac_leakage_table) when it
should have been multiplied it by sizeof(struct phm_cac_leakage_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/5f7c5d38.iT%2FQTjN+659XUDo5%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

@@ -393,7 +393,7 @@ union phm_cac_leakage_record {
 
 struct phm_cac_leakage_table {
 	uint32_t count;
-	union phm_cac_leakage_record entries[1];
+	union phm_cac_leakage_record entries[];
 };
 
 struct phm_samu_clock_voltage_dependency_record {

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

@@ -1384,17 +1384,14 @@ static int get_cac_leakage_table(struct pp_hwmgr *hwmgr,
 				const ATOM_PPLIB_CAC_Leakage_Table *table)
 {
 	struct phm_cac_leakage_table  *cac_leakage_table;
-	unsigned long            table_size, i;
+	unsigned long i;
 
-	if (hwmgr == NULL || table == NULL || ptable == NULL)
+	if (!hwmgr || !table || !ptable)
 		return -EINVAL;
 
-	table_size = sizeof(ULONG) +
-		(sizeof(struct phm_cac_leakage_table) * table->ucNumEntries);
-
-	cac_leakage_table = kzalloc(table_size, GFP_KERNEL);
-
-	if (cac_leakage_table == NULL)
+	cac_leakage_table = kzalloc(struct_size(cac_leakage_table, entries, table->ucNumEntries),
+				    GFP_KERNEL);
+	if (!cac_leakage_table)
 		return -ENOMEM;
 
 	cac_leakage_table->count = (ULONG)table->ucNumEntries;