Fix the following checkpatch warnings observed in mailbox module.

WARNING: please, no space for starting a line,
                                excluding comments
+ fail_alloc_rxq:$

WARNING: please, no space for starting a line,
                                excluding comments
+ fail_alloc_txq:$

WARNING: please, no space for starting a line,
                                excluding comments
+ fail_request_irq:$

WARNING: line over 80 characters
+       mbox_kfifo_size = max_t(unsigned int, mbox_kfifo_size, sizeof(mbox_msg_t));
Signed-off-by: Hari Kanigeri <h-kanigeri2@ti.com>
Acked-by: Hiroshi Doyu <hiroshi.doyu@nokia.com>