microcode: fix section mismatch warning

Fix the following section mismatch warnings in microcode.c:
WARNING: arch/i386/kernel/built-in.o(.init.text+0x3966): Section mismatch: reference to .exit.text: (between 'microcode_init' and 'parse_maxcpus')
WARNING: arch/i386/kernel/built-in.o(.init.text+0x3992): Section mismatch: reference to .exit.text: (between 'microcode_init' and 'parse_maxcpus')

The warning are caused by a function marked __init that
calls a function marked __exit.
Functions marked __exit may be discarded either during link or run-time
and thus the reference is not good.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>