bnxt_en: Add hwrm_send_message_silent().

This is used to send NVM_FIND_DIR_ENTRY messages which can return error
if the entry is not found.  This is normal and the error message will
cause unnecessary alarm, so silence it.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>