debugcon: fix compiler warning when open DEBUG_DEBUGCON

debugcon: fix compiler warning when open DEBUG_DEBUGCON

compiler warnings:
  CC    hw/char/debugcon.o
hw/char/debugcon.c: In function ‘debugcon_ioport_write’:
hw/char/debugcon.c:58: warning: format ‘%02x’ expects type ‘unsigned int’, but argument 3 has type ‘uint64_t’
hw/char/debugcon.c: In function ‘debugcon_ioport_read’:
hw/char/debugcon.c:70: warning: format ‘%04x’ expects type ‘unsigned int’, but argument 2 has type ‘hwaddr’

Signed-off-by: liguang <lig.fnst@cn.fujitsu.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>