SLI-4 does not contain a PORT_CAPABILITIES mailbox command (only SLI-3
does, and SLI-3 doesn't use it), yet there are SLI-4 code paths that have
code to issue the command.  The command will always fail.

Remove the code for the mailbox command and leave only the resulting
"failure path" logic.

Link: https://lore.kernel.org/r/20210412013127.2387-12-jsmart2021@gmail.comCo-developed-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>