matroxfb: avoid -Warray-bounds warning

The open-coded list_for_each_entry() causes a harmless warning:

drivers/video/fbdev/matrox/matroxfb_base.c: In function 'matroxfb_register_driver':
include/linux/kernel.h:856:3: warning: array subscript -98 is outside array bounds of 'struct list_head[1]' [-Warray-bounds]

Use the normal list_for_each_entry instead.

Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201026194010.3817166-1-arnd@kernel.org