habanalabs: Avoid running restore chunks if no execute chunks

CS with no chunks for execute phase is invalid, so its
context_switch/restore phase should not be run.
Hence, move the check of the execute chunks number to the beginning of
hl_cs_ioctl().

Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>