drm/amdkfd: Use ARRAY_SIZE macro in kfd_build_sysfs_node_entry

Use ARRAY_SIZE instead of dividing sizeof array with sizeof an element.

This issue was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Reviewed-by: Felix <Kuehling&lt;Felix.Kuehling@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>