ARM: OMAP1: ams-delta: register MODEM device earlier

Amstrad Delta MODEM device used to be initialized at arch_initcall
before it was once moved to late_initcall by commit f7519d8c ("ARM:
OMAP1: ams-delta: register latch dependent devices later"). The purpose
of that change was to postpone initialization of devices which depended
on latch2 pins until latch2 converted to GPIO device was ready.

After recent fixes to GPIO handling, it was possible to moove
registration of most of those device back to where they were before.
The same can be safely done with the MODEM device as initialization
of GPIO pins it depends on was moved to machine_init by preceding
patch.

Move registration of the MODEM device to arch_initcall_sync, not to
arch_initcall, so it is never exposed to potential conflict in
registration order hazard against OMAP serial ports.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>