sh: fix build error in board-sh7757lcr.c

Fix the problem that the sh_mobile_sdhi.h changed the directory from
"linux/mfd/" to "linux/mmc/".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>