virtual_eisa_root_init() should be __init

WARNING: vmlinux - Section mismatch: reference to
.init.text:eisa_root_register from .text between 'virtual_eisa_root_init' (at
offset 0xc026b80f) and 'cpufreq_debug_disable_ratelimit'

Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>