util: fix thinko in runIO

When aligning you need to clear the bits in the mask and leave the
others aside.  Likely this code has never run, and will never run.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

src/util/iohelper.c

@@ -98,7 +98,7 @@ runIO(const char *path, int fd, int oflags, unsigned long long length)
         goto cleanup;
     }
     base = buf;
-    buf = (char *) (((intptr_t) base + alignMask) & alignMask);
+    buf = (char *) (((intptr_t) base + alignMask) & ~alignMask);
 #endif
 
     switch (oflags & O_ACCMODE) {