bnxt_en: return proper error when FW returns HWRM_ERR_CODE_RESOURCE_ACCESS_DENIED

Return proper error code when Firmware returns
HWRM_ERR_CODE_RESOURCE_ACCESS_DENIED for HWRM_NVM_GET/SET_VARIABLE
commands.

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