[U-Boot-Users] [patch] fix lib_generic version of strswab()

This patch changes the behavior of strswab() to end the byte swapping when either of the two candidate bytes is null. The old behavior was to only abort when the second byte was null. It looks like this is only used for little endian machines running with CONFIG_IDE.

I noticed this because the ide serial number was not printing out - the reason was strswab() was running past the end of the previous string in memory and swapping a null into the first byte of my serial number string.