mqueue: fix compilation error when CONFIG_DISABLE_MQUEUE=y
This patch fixes compilation error when CONFIG_DISABLE_MQUEUE is
enabled.
In file included from group/group_leave.c:71:0:
./mqueue/mqueue.h:73:5: error: "CONFIG_MQ_MAXMSGSIZE" is not defined [-Werror=undef]
#if CONFIG_MQ_MAXMSGSIZE > 0
^
cc1: all warnings being treated as errors
#include <tinyara/mqueue.h>
-#if CONFIG_MQ_MAXMSGSIZE > 0
+#if !defined(CONFIG_DISABLE_MQUEUE) && CONFIG_MQ_MAXMSGSIZE > 0
/****************************************************************************
* Pre-processor Definitions
