crypto: arm/sha1 - Fix clang function cast warnings

Instead of casting the function which upsets clang for some reason,
change the assembly function siganture instead.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>