habanalabs: bugs fixes in timestamps buff alloc

use argument instead of fixed GFP value for allocation
in Timestamps buffers alloc function.
change data type of size to size_t.

Fixes: 9158bf69

 ("habanalabs: Timestamps buffers registration")
Signed-off-by: farah kassabri <fkassabri@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>