jsm: remove the ch_custom_speed field

Currently the ch_custom_speed field exists but is never used,
so, this patch removes it.

Signed-off-by: Breno Leitão <leitao@linux.vnet.ibm.com>
Cc: Scott Kilau <scottk@digi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>