Revise recent changes to serial driver error handling: Errors other than...

Revise recent changes to serial driver error handling:  Errors other than EINTR may be returned when the driver is used very early in initialization.  STM32 SPI driver will now survive repeated initializations

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5026 42af7a65-404d-4744-a932-0658087f49c3