warning: fix init do_mounts_md c

fix warning:

  init/do_mounts_md.c: In function ‘md_run_setup’:
  init/do_mounts_md.c:282: warning: ISO C90 forbids mixed declarations and code

also, use the opportunity to put the RAID autodetection code
into a separate function - this also solves a checkpatch style warning.

No code changed:

md5:
   aa36a35faef371b05f1974ad583bdbbd  do_mounts_md.o.before.asm
   aa36a35faef371b05f1974ad583bdbbd  do_mounts_md.o.after.asm

Signed-off-by: Ingo Molnar <mingo@elte.hu>