ntoskrnl: Have MmIsAddressValid use IsBadReadPtr.

dlls/ntoskrnl.exe/ntoskrnl.c

@@ -2164,7 +2164,7 @@ void WINAPI MmFreeNonCachedMemory( void *addr, SIZE_T size )
 BOOLEAN WINAPI MmIsAddressValid(PVOID VirtualAddress)
 {
     TRACE("(%p)\n", VirtualAddress);
-    return !IsBadWritePtr(VirtualAddress, 1);
+    return !IsBadReadPtr(VirtualAddress, 1);
 }
 
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