ARM: pxa: remove __init from cpufreq_driver->init()

This is causing section mismatches when linking, as cpufreq_driver->init()
is not supposed to be in init section.

Reported-by: Tomáš 'Sleep_Walker' Čech <sleep_walker@suse.cz>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>