serial: ioremap warning fix for jsm driver.

I saw a warning about ioremap from the jsm driver on a system which
looked like this:

resource map sanity check conflict: 0xe0200800 0xe02017ff 0xe0200800 0xe0200fff 0000:01:08.0

Turns out the warning is valid.  The jsm driver has been asking to ioremap
0x1000 forever, but in fact only 8 port chips have 0x1000 bytes of memory.
4 port chips have 0x800 and 2 port chips have 0x400 according to the
data sheet.  It makes more sense to map the size of the region rather
than a hard coded value.  If you happen to have the region legitimately
mapped to a base address that is not 4K aligned, ioremap complains
otherwise.

Signed-off-by: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>