fbdev: sm712fb: handle ioremap() errors in probe

smtcfb_pci_probe() does not handle ioremap() errors for case 0x720. The
patch fixes that exactly like for case 0x710/2.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200713080532.15504-1-novikov@ispras.ru