Fix signature of the waveInProc/waveOutProc callbacks.

Parameters are DWORD_PTR instead of DWORD, which did not matter
on 32bit but caused MinGW64-compiler warnings and potential
crashes on 64bit.

Change-Id: I840ae3ea7ea532746f73f20b3233cae842931d45
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
(cherry picked from qtmultimedia/699a5d75aab2de7e2c341be8533446597bee355e)
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Multimedia: Fix MinGW-warning about assigning NULL to int-type.

Change-Id: I58fc7628845ed0733b79af5ab89c360ab8a12863
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>