bnxt_en: Fix build error for kernesl without RTC-LIB

bnxt_hwrm_fw_set_time() now returns -EOPNOTSUPP when built for kernel
without RTC_LIB.  Setting the firmware time is not critical to the
successful completion of the firmware update process.

Signed-off-by: Rob Swindell <Rob.Swindell@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>