staging: dgnc: tty.c: updates uart_struct declaration for sparse

This patch edits the type casts neo_uart_struct and
cls_uart_struct. A previous patch added the marker __iomem
to these structs. This patch ensures that the change to
the marker is consistent. This also removes these
sparse warnings:

warning: incorrect type in assignment (different address spaces)
  expected struct neo_uart_struct [noderef] <asn:2>*ch_neo_uart
  got struct neo_uart_struct *<noident>
warning: incorrect type in assignment (different address spaces)
  expected struct cls_uart_struct [noderef] <asn:2>*ch_cls_uart
  got struct cls_uart_struct *<noident>

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>