habanalabs: prevent user buff overflow

This commit fixes a potential debugfs issue that may occur when
reading the clock gating mask into the user buffer since the
user buffer size was not taken into consideration.

Signed-off-by: Moti Haimovski <mhaimovski@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>