mmc: bfin_sdh: fix unused sg warning on BF51x/BF52x systems

The local sg variable is only used with BF54x code.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>