Replace psa_unlock_key_slot calls in operations which act on FULL slots

Replaces calls to psa_unlock_key_slot with calls to psa_unregister_read.

All instances follow a pattern of a call to psa_get_and_lock_key_slot_X,
followed by some code which reads from a slot, followed by a call to psa_unregister_read.

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index 3d997a5..3c16de3 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -516,7 +516,7 @@
 
     *handle = key;
 
-    return psa_unlock_key_slot(slot);
+    return psa_unregister_read(slot);
 
 #else /* MBEDTLS_PSA_CRYPTO_STORAGE_C || MBEDTLS_PSA_CRYPTO_BUILTIN_KEYS */
     (void) key;