msacm32.drv: Constify some variables

[Andrew Talbot]

Changelog:
    msacm32.drv: Constify some variables.

diff -urN a/dlls/msacm32.drv/wavemap.c b/dlls/msacm32.drv/wavemap.c
--- a/dlls/msacm32.drv/wavemap.c	2006-10-10 12:51:39.000000000 +0100
+++ b/dlls/msacm32.drv/wavemap.c	2007-05-27 17:25:59.000000000 +0100
@@ -67,7 +67,7 @@
     DWORD       nSamplesPerSecInner;
 } WAVEMAPDATA;
 
-static	BOOL	WAVEMAP_IsData(WAVEMAPDATA* wm)
+static	BOOL	WAVEMAP_IsData(const WAVEMAPDATA* wm)
 {
     return (!IsBadReadPtr(wm, sizeof(WAVEMAPDATA)) && wm->self == wm);
 }