Fix incorrect error checking of prvCreateIdleTasks (#1158)

Fix incorrect error checking of prvCreateIdleTasks (#1158)

In environments that do not support static allocation
(configSUPPORT_STATIC_ALLOCATION == 0), at prvCreateIdleTasks(), call
xCreateTask() and compare its return value to pdFAIL to check whether
xCreateTask() failed. However, xCreateTask() returns
errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY as the error value, so the
result of this comparison is always false.

This commit fixes this problem by changing the return value comparison
to pdPASS instead of pdFAIL.