zfs: missing newline character in zfs_do_channel_program() error message

zfs: missing newline character in zfs_do_channel_program() error message

This commit simply adds a missing newline ("\n") character to the error
message printed by the zfs command when the provided pool parameter
can't be found.

Reviewed-by: Chris Dunlop <chris@onthe.net.au>
Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #8783