drm/gma500: Fix null dereference in hdmi teardown

pci_set_drvdata sets the value of pdev->driver_data to NULL,
after which the driver_data obtained from the same dev is
dereferenced in oaktrail_hdmi_i2c_exit, and the i2c_dev is
extracted from it. To prevent this, swap these calls.

Found by Linux Verification Center (linuxtesting.org) with Svacer.

Fixes: 1b082ccf ("gma500: Add Oaktrail support")
Signed-off-by: Zabelin Nikita <n.zabelin@mt-integration.ru>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://lore.kernel.org/r/20250918150703.2562604-1-n.zabelin@mt-integration.ru