alpha: fix two section mismatch warnings

Fix the following section mismatch warnings:

WARNING: o-alpha/vmlinux.o(.text+0x1a4d4): Section mismatch: reference to .init.text:free_area_init (between 'paging_init' and 'srm_paging_stop')
WARNING: o-alpha/vmlinux.o(.text+0x1a4dc): Section mismatch: reference to .init.text:free_area_init (between 'paging_init' and 'srm_paging_stop')

One instance of paging_init() was declared __init but not the other one -
used by defconfig.  Fixed by declaring the second instance ___init too.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>