drm/amdkfd: Fix wrong usage of INIT_WORK()

In kfd_procfs_show(), the sdma_activity_work_handler is a local variable
and the sdma_activity_work_handler.sdma_activity_work should initialize
with INIT_WORK_ONSTACK() instead of INIT_WORK().

Fixes: 32cb59f3 ("drm/amdkfd: Track SDMA utilization per process")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Signed-off-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>