ltc: bugfix find_prng()

When the prng_descriptor was changed to a pointer to descriptors in
7892cb1
"ltc: make prng_descriptor a pointer to descriptors"
wasn't the find_prng() updated properly.
This causes NULL pointer error if
the PRNG name isn't found before the list is exhausted. This patch
fixes this problem.

Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: David Brown <david.brown@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

core/lib/libtomcrypt/src/misc/crypt/crypt_find_prng.c

@@ -53,7 +53,7 @@ int find_prng(const char *name)
    LTC_ARGCHK(name != NULL);
    LTC_MUTEX_LOCK(&ltc_prng_mutex);
    for (x = 0; x < TAB_SIZE; x++) {
-       if ((prng_descriptor[x]->name != NULL) && XSTRCMP(prng_descriptor[x]->name, name) == 0) {
+       if ((prng_descriptor[x] != NULL) && XSTRCMP(prng_descriptor[x]->name, name) == 0) {
           LTC_MUTEX_UNLOCK(&ltc_prng_mutex);
           return x;
        }