xtensa: xtfpga: fix section mismatch

platform_calibrate_ccount() calls update_clock_frequency() which is in .init
section. However, platform_calibrate_ccount() itself is only called from .init
(i.e., time_init()).

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>