drm/amdgpu: fix a potential information leaking bug

Coccinelle reports a path that the array "data" is never initialized.
The path skips the checks in the conditional branches when either
of callback functions, read_wave_vgprs and read_wave_sgprs, is not
registered. Later, the uninitialized "data" array is read
in the while-loop below and passed to put_user().

Fix the path by allocating the array with kcalloc().

The patch is simplier than adding a fall-back branch that explicitly
calls memset(data, 0, ...). Also it does not need the multiplication
1024*sizeof(*data) as the size parameter for memset() though there is
no risk of integer overflow.

Signed-off-by: Wang Xiayang <xywang.sjtu@sjtu.edu.cn>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c

@@ -707,7 +707,7 @@ static ssize_t amdgpu_debugfs_gpr_read(struct file *f, char __user *buf,
 	thread = (*pos & GENMASK_ULL(59, 52)) >> 52;
 	bank = (*pos & GENMASK_ULL(61, 60)) >> 60;
 
-	data = kmalloc_array(1024, sizeof(*data), GFP_KERNEL);
+	data = kcalloc(1024, sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;