drm/ast: Fix missing conversions to managed API

drm/ast: Fix missing conversions to managed API

BugLink: https://bugs.launchpad.net/bugs/1938340
[ Upstream commit 9ea172a9a3f4a7c5e876469509fc18ddefc7d49d ]

The commit 7cbb93d89838 ("drm/ast: Use managed pci functions")
converted a few PCI accessors to the managed API and dropped the
manual pci_iounmap() calls, but it seems to have forgotten converting
pci_iomap() to the managed one.  It resulted in the leftover resources
after the driver unbind.  Let's fix them.

Fixes: 7cbb93d89838 ("drm/ast: Use managed pci functions")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210421170458.21178-1-tiwai@suse.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>