habanalabs: use the user CB size as a default job size

When no patched command buffer (CB) is created, use the user CB size as
the job size.

Signed-off-by: Omer Shpigelman <oshpigelman@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>