mini-os: tpm: fix array access in locality_enabled

gcc-4.3 fails to prove that array indices will remain positive. Add a
hint for the compiler and check the index value before using it.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

extras/mini-os/tpm_tis.c

@@ -611,7 +611,7 @@ s_time_t tpm_calc_ordinal_duration(struct tpm_chip *chip,
 
 
 static int locality_enabled(struct tpm_chip* tpm, int l) {
-   return tpm->enabled_localities & (1 << l);
+   return l >= 0 && tpm->enabled_localities & (1 << l);
 }
 
 static int check_locality(struct tpm_chip* tpm, int l) {