jsm: removing ch_old_baud field

Currently the field jsm_channel->ch_old_baud is not used, just
assigned in a lot of places but never used. This patches removes
this field.

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>