crypto: octeontx2 - out of bounds access in otx2_cpt_dl_custom_egrp_delete()

If "egrp" is negative then it is causes an out of bounds access in
eng_grps->grp[].

Fixes: d9d77497

 ("crypto: octeontx2 - add apis for custom engine groups")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>