UPSTREAM: crypto: x86/curve25519 - Remove unused carry variables

The carry variables are assigned but never used, which upsets
the compiler.  This patch removes them.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Karthikeyan Bhargavan <karthik.bhargavan@gmail.com>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
(cherry picked from commit 054a5540fb8f7268e2c79e9deab4242db15c8cba)
Bug: 152722841
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ia581bdb636cdc24fe0b3d6cb9f95557221405ee7