ci: update SCP binary path

Use the current latest version of 2.15.0,
please find the tag for this version at
https://gitlab.arm.com/firmware/SCP-firmware/-/tree/v2.15.0?ref_type=tags

Signed-off-by: Ryan Everett <ryan.everett@arm.com>
Change-Id: Ia0242e20e56131b4dd3681d2e05749924cca5d73
1 file changed