nvme: use argconfig_parse_comma_sep_array_u16() in attach-ns

nvme: use argconfig_parse_comma_sep_array_u16() in attach-ns

nvme_attach_ns() is using argconfig_parse_comma_sep_array()
to parse a list of ints and then copying them into a list of u16s.

Use argconfig_parse_comma_sep_array_u16() instead to save on memory
and avoid needing to copy the values to another list.
This also checks that the values fit in u16.

Also use NVME_ID_CTRL_LIST_MAX instead of hard-coding the max list size.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>