This replaces the plain loop over the sglist array with for_each_sg()
macro which consists of sg_next() function calls.  Since m68k doesn't
select ARCH_HAS_SG_CHAIN, it is not necessary to use for_each_sg() in
order to loop over each sg element.  But this can help find problems
with drivers that do not properly initialize their sg tables when
CONFIG_DEBUG_SG is enabled.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-arch@vger.kernel.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>