crypto: omap - Drop obsolete PageSlab check

As it is now legal to call flush_dcache_page on slab pages we
no longer need to do the check in the omap driver.  This patch
also uses flush_dcache_page instead of flush_kernel_dcache_page
because the page we're writing to could be anything.

Reported-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>