Fix

WARNING: arch/arm/plat-omap/built-in.o - Section mismatch: reference
to .init.text: from .text between 'dsp_cpustat_update' (at offset
0x7c40) and 'do_release_mem'

If init_dsp isn't set, dsp_cpustat_update() calls omap_dsp_init(). So
don't declare omap_dsp_init() as __init.

Signed-off-by: Dirk Behme <dirk.behme@gmail.com>