crypto: bpf - Add MODULE_DESCRIPTION for skcipher

All modules should have a description, building with extra warnings
enabled prints this outfor the for bpf_crypto_skcipher module:

WARNING: modpost: missing MODULE_DESCRIPTION() in crypto/bpf_crypto_skcipher.o

Add a description line.

Fixes: fda4f712 ("bpf: crypto: add skcipher to bpf crypto")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>