bnxt_en: fix read of stored FW_PSID version on P5 devices

P5 devices store NVM arrays using a different internal representation.
This implementation detail permeates into the HWRM API, requiring the
caller to explicitly index the array elements in HWRM_NVM_GET_VARIABLE
on these devices. Conversely, older devices do not support the indexed
mode of operation and require reading the raw NVM content.

Fixes: db28b6c7 ("bnxt_en: Fix devlink info's stored fw.psid version format.")
Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>