cabinet: Constify some variables (2 of 3)

[Andrew Talbot]

Changelog:
    cabinet: Constify some variables.

diff -urN a/dlls/cabinet/fci.c b/dlls/cabinet/fci.c
--- a/dlls/cabinet/fci.c	2006-12-15 17:25:55.000000000 +0000
+++ b/dlls/cabinet/fci.c	2007-03-14 20:03:32.000000000 +0000
@@ -430,12 +430,12 @@
 
 
 
-static cab_ULONG fci_get_checksum(void *pv, UINT cb, CHECKSUM seed)
+static cab_ULONG fci_get_checksum(const void *pv, UINT cb, CHECKSUM seed)
 {
-  cab_ULONG csum;
-  cab_ULONG ul;
-  int       cUlong;
-  BYTE      *pb;
+  cab_ULONG     csum;
+  cab_ULONG     ul;
+  int           cUlong;
+  const BYTE    *pb;
 
   csum = seed;
   cUlong = cb / 4;