bnxt_en: Suppress HWRM errors for HWRM_NVM_GET_VARIABLE command

For newly added NVM parameters, older firmware may not have the support.
Suppress the error message to avoid the unncessary error message which is
triggered when devlink calls the driver during initialization.

Fixes: 782a624d ("bnxt_en: Add bnxt_en initial params table and register it.")
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>