PCnet: Fix section mismatch

Building MIPS mtx1_defconfig results in:

  MODPOST 735 modules
WARNING: drivers/net/pcnet32.o(.devinit.text+0x11ec): Section mismatch in reference from the function pcnet32_probe_vlbus.constprop.22() to the variable .init.data:pcnet32_portlist
The function __devinit pcnet32_probe_vlbus.constprop.22() references
a variable __initdata pcnet32_portlist.
If pcnet32_portlist is only used by pcnet32_probe_vlbus.constprop.22 then
annotate pcnet32_portlist with a matching annotation.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>