Fix signed/unsigned comparison warnings.

diff --git a/dlls/advapi32/registry.c b/dlls/advapi32/registry.c
index 404d5a8..004ba50 100644
--- a/dlls/advapi32/registry.c
+++ b/dlls/advapi32/registry.c
@@ -663,7 +663,7 @@
 DWORD WINAPI RegQueryMultipleValuesA(HKEY hkey, PVALENTA val_list, DWORD num_vals,
                                      LPSTR lpValueBuf, LPDWORD ldwTotsize)
 {
-    int i;
+    unsigned int i;
     DWORD maxBytes = *ldwTotsize;
     HRESULT status;
     LPSTR bufptr = lpValueBuf;
@@ -709,7 +709,7 @@
 DWORD WINAPI RegQueryMultipleValuesW(HKEY hkey, PVALENTW val_list, DWORD num_vals,
                                      LPWSTR lpValueBuf, LPDWORD ldwTotsize)
 {
-    int i;
+    unsigned int i;
     DWORD maxBytes = *ldwTotsize;
     HRESULT status;
     LPSTR bufptr = (LPSTR)lpValueBuf;