It is important to know why a firmware command failed. Hence log 'rval'
together with the values of the mailbox registers if a firwmare command
fails.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Cc: Giridhar Malavali <gmalavali@marvell.com>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Acked-by: NHimanshu Madhani <hmadhani@marvell.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>