examples/l2fwd-crypto: fix stats array length

examples/l2fwd-crypto: fix stats array length

crypto_statistics array was not big enough for storing
all the possible crypto device statistics, as its size was
RTE_MAX_ETHPORTS, but should be RTE_CRYPTO_MAX_DEVS, leading
this to a potential out-of-bounds issue.

Coverity issue: 120145
Fixes: 387259bd6c67 ("examples/l2fwd-crypto: add sample application")

Signed-off-by: Slawomir Mrozowicz <slawomirx.mrozowicz@intel.com>
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>