qed*: Fix size of config attribute dump.

Driver currently returns max-buf-size as size of the config attribute.
This patch incorporates changes to read this value from MFW (if available)
and provide it to the user. Also did a trivial clean up in this path.

Fixes: d44a3ced ("qede: Add support for reading the config id attributes.")
Signed-off-by: Sudarsana Reddy Kalluru <skalluru@marvell.com>
Signed-off-by: Ariel Elior <aelior@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>