mmc, sh: Correct value for reset

This resolves a regression that I introduced in
"mmc, sh: Move constants to sh_mmcif.h". Having
examined the manual and tested the code on an AP4EVB board
it seems that the correct sequence is.

1) Write 1 to bit 31 and zeros to all other bits
2) Write zero to all bits

Cc: Yusuke Goda <yusuke.goda.sx@renesas.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>