mm/slab_common.c: make calculate_alignment() static

mm/slab_common.c: make calculate_alignment() static

calculate_alignment() function is only used inside slab_common.c.  So
make it static and let the compiler do more optimizations.

After this patch there's a small improvement in text and data size.

  $ gcc --version
    gcc (GCC) 7.2.1 20171128

Before:
  text	   data	    bss	    dec	     hex	filename
  9890457  3828702  1212364 14931523 e3d643	vmlinux

After:
  text	   data	    bss	    dec	     hex	filename
  9890437  3828670  1212364 14931471 e3d60f	vmlinux

Also I fixed a style problem reported by checkpatch.

  WARNING: Missing a blank line after declarations
  #53: FILE: mm/slab_common.c:286:
  +		unsigned long ralign = cache_line_size();
  +		while (size <= ralign / 2)

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Byongho Lee <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>