fbdev: kyro: Use devm_ioremap_wc() for screen mem

Replace the manual pci_ioremap_wc() call for mapping screen memory with the
device-managed devm_ioremap_wc() variant.

This simplifies the driver's resource management by ensuring the memory is
automatically unmapped when the driver detaches from the device.

Signed-off-by: Giovanni Di Santi <giovanni.disanti.lkl@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>