mailbox: Fix a couple of trivial static checker issues

This patch deals with a few spelling, white space and type
warnings reported by Intel's Kbuild Test Robot.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
diff --git a/drivers/mailbox/mailbox-sti.c b/drivers/mailbox/mailbox-sti.c
index f11d4e8..4835817 100644
--- a/drivers/mailbox/mailbox-sti.c
+++ b/drivers/mailbox/mailbox-sti.c
@@ -64,7 +64,7 @@
 };
 
 /**
- * STi Mailbox platform specfic configuration
+ * STi Mailbox platform specific configuration
  *
  * @num_inst:	Maximum number of instances in one HW Mailbox
  * @num_chan:	Maximum number of channel per instance