crypto: mips: add poly1305-core.S to .gitignore

poly1305-core.S is an auto-generated file, so it should be ignored.

Fixes: a11d055e7a64 ("crypto: mips/poly1305 - incorporate OpenSSL/CRYPTOGAMS optimized implementation")
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>