MFC r264800: fixes for problems found by Coverity scan...   - Get transmit loop more in line with the other serial drivers.   - Add a comment about FTDI and ZLPs.   - Correctly check odditiy of baud rate divisor.   - Correct IOCTL handling for "error" and "event" char.
MFC r264800: fixes for problems found by Coverity scan...
  - Get transmit loop more in line with the other serial drivers.
  - Add a comment about FTDI and ZLPs.
  - Correctly check odditiy of baud rate divisor.
  - Correct IOCTL handling for "error" and "event" char.

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