debugcon: fix always print "addr=0x0, val=0x0" bug when use DEBUG_DEBUGCON

when use DEBUG_DEBUGCON, screen spits:
debugcon: write addr=0x0000 val=0x00
Rdebugcon: write addr=0x0000 val=0x00
udebugcon: write addr=0x0000 val=0x00
ndebugcon: write addr=0x0000 val=0x00
ndebugcon: write addr=0x0000 val=0x00
idebugcon: write addr=0x0000 val=0x00
ndebugcon: write addr=0x0000 val=0x00
gdebugcon: write addr=0x0000 val=0x00
 debugcon: write addr=0x0000 val=0x00
odebugcon: write addr=0x0000 val=0x00
pdebugcon: write addr=0x0000 val=0x00
tdebugcon: write addr=0x0000 val=0x00
idebugcon: write addr=0x0000 val=0x00
odebugcon: write addr=0x0000 val=0x00
ndebugcon: write addr=0x0000 val=0x00
 debugcon: write addr=0x0000 val=0x00
rdebugcon: write addr=0x0000 val=0x00
odebugcon: write addr=0x0000 val=0x00
mdebugcon: write addr=0x0000 val=0x00
 debugcon: write addr=0x0000 val=0x00
adebugcon: write addr=0x0000 val=0x00
tdebugcon: write addr=0x0000 val=0x00
 debugcon: write addr=0x0000 val=0x00

Oh, that's wrong, val is not always be 0.
this bug caused by lack of length modifier
for specifier 'x'.
Signed-off-by: Nliguang <lig.fnst@cn.fujitsu.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/char/debugcon.c

@@ -55,7 +55,7 @@ static void debugcon_ioport_write(void *opaque, hwaddr addr, uint64_t val,
     unsigned char ch = val;
 
 #ifdef DEBUG_DEBUGCON
-    printf("debugcon: write addr=0x%04x val=0x%02x\n", addr, val);
+    printf("debugcon: write addr=0x%04" HWADDR_PRIx " val=0x%02x\n", addr, val);
 #endif
 
     qemu_chr_fe_write(s->chr, &ch, 1);