speaker-test.c - fix sine generator on big-endian archs

speaker-test.c - fix sine generator on big-endian archs

speaker-test doesn't work well when you choose a little-endian format on a
big-endian processor, or the opposite. Yes, I know about plughw:, but for
debugging purposes it may not be an option. The following patch add proper
support for S32 and S16 support for but LE and BE processors:

- The "if (bits-per-sample)" construct was replaced by case (format).
- Support for S16_BE, S32_BE formats was added.
- S16_LE and S32_LE were made compatible with big-endian processors.
- NB: The pink noise generator wasn't changed (I'll do if this patch is OK).

From: Giuliano Pochini <pochini@shiny.it>