Alsa support for Maemo SDK (n770) - Remove compile warnings

Alsa support for Maemo SDK (n770) - Remove compile warnings

    Here is a patch to remove compile warnings. It must be applied
after last patch set I sent.
    This patch simply changes signedness of some point from the code
to match the correct sign used by dsp-protocol structures. All must
use unsigned variables.
    It also changes the way the pthread_mutex is initialized. The
warning about pthreads is also removed.

    I tested the compilation with:
gcc (GCC) 4.1.2 20061028 (prerelease) (Debian 4.1.1-19)
and
sbox-arm-linux-gcc (GCC) 3.4.4 (release) (CodeSourcery ARM 2005q3-2)

Signed-off-by: Eduardo Valentin <eduardo.valentin@indt.org.br>