crypto: omap-des - make local functions static

Make omap_des_copy_needed(), omap_des_copy_sgs(), because these
functions are used only in this file.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Joel Fernandes <joelf@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>