be2net: make be_cmd_get_regs() return a status

There are a few failure cases in be_cmd_get_regs() that ideally must return
an error value. This style is used across all the routines in be_cmds.c with
this routine being an exception. This patch fixes this.

Signed-off-by: Vasundhara Volam <vasundhara.volam@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>