leverage psa_allocate_buffer_to_slot from slot management

It makes the implementation of psa_load_builtin_key_into_slot a lot
cleaner.

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 32568b3..068990a 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -604,20 +604,8 @@
     return( PSA_ERROR_INVALID_ARGUMENT );
 }
 
-/** Try to allocate a buffer to an empty key slot.
- *
- * \param[in,out] slot          Key slot to attach buffer to.
- * \param[in] buffer_length     Requested size of the buffer.
- *
- * \retval #PSA_SUCCESS
- *         The buffer has been successfully allocated.
- * \retval #PSA_ERROR_INSUFFICIENT_MEMORY
- *         Not enough memory was available for allocation.
- * \retval #PSA_ERROR_ALREADY_EXISTS
- *         Trying to allocate a buffer to a non-empty key slot.
- */
-static psa_status_t psa_allocate_buffer_to_slot( psa_key_slot_t *slot,
-                                                 size_t buffer_length )
+psa_status_t psa_allocate_buffer_to_slot( psa_key_slot_t *slot,
+                                          size_t buffer_length )
 {
     if( slot->key.data != NULL )
         return( PSA_ERROR_ALREADY_EXISTS );