sh: fix up an off-by-1 in the number of early ioremap fixmaps.

There was an off-by-1 in the begin/end of the ioremap fixmaps, leaving us
with a spurious entry. In practice this wasn't a problem since we aligned
on a PMD boundary anyways, but this makes it consistent with the
intention and the other fixmaps.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>