Remove Dangerous Parameter Passing

Another coverity bug - #350039

When this test discovers a key of the wrong type, it still throws it
through the export function in order to check that it too will detect
this as a not permitted action. For the buffer and buffer length
arguments it passes in a local pointer (which will most likely be NULL),
and the sizeof that pointer, as it knows that they will never be used.
Coverity rightly (imho) flagged this as suspicious - if we are going to
pass in incorrect parameters, at least make them obviously incorrect, and
ones that will not potentially cause errors if the code later changes.
There is, for example safety checks for zero length buffer, but less
protection for an insufficiently sized one.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

tests/suites/test_suite_psa_crypto_slot_management.function

@@ -270,7 +270,7 @@ void persistent_slot_lifecycle( int lifetime_arg, int id_arg,
             else
             {
                 TEST_EQUAL( psa_export_key( handle,
-                                            reexported, sizeof( reexported ),
+                                            NULL, 0,
                                             &reexported_length ),
                             PSA_ERROR_NOT_PERMITTED );
             }