fix: fix call to `FFA_VERSION`

`SKIP_TEST_IF_FFA_VERSION_LESS_THAN` was attempting to change the FF-A
version, when it only needed to query it. The recent change to
`FFA_VERSION` means that attempting to change the version would fail.

Signed-off-by: Karl Meakin <karl.meakin@arm.com>
Change-Id: Id8572d1a4d61b17a85af44f96e3720230d35e698
1 file changed