spi: omap2: use SUPERH, not SH

Commit 0079aae0 ("spi: omap2: Add build dependencies for
writel_relaxed()") added an optional Kconfig dependency on SH. That
Kconfig symbol doesn't exist. Apparently SUPERH was intended. Use that.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@linaro.org>