bnxt_en: Modify some bnxt_hwrm_*_free() functions to void.

Return code is not needed in some of these functions, as the return
code from firmware message is ignored. Remove the unused rc variable
and also convert functions to void.

Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>