MIPS: atomic.h: Reformat to fit in 79 columns

Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8484/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>