staging: slicoss: ensure mapping of io-memory is uncached

Writes to registers should be done uncached for various reasons. Ensure
this by replacing ioremap() with ioremap_nocache().

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>