Fix: correct Linux FF-A driver dependency

Currently the TS->Linux driver dependency is set to the tip of the main
branch of the driver. Since the branch has moved correction is needed to
driver API version 1.0.0.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: Ie2d9e4fa13dc6d860a779ab8f89a28af944aebb0
diff --git a/external/LinuxFFAUserShim/LinuxFFAUserShim.cmake b/external/LinuxFFAUserShim/LinuxFFAUserShim.cmake
index 565017b..7deaf69 100644
--- a/external/LinuxFFAUserShim/LinuxFFAUserShim.cmake
+++ b/external/LinuxFFAUserShim/LinuxFFAUserShim.cmake
@@ -18,7 +18,7 @@
 	else()
 		set(LINUX_FFA_USER_SHIM_URL "https://git.gitlab.arm.com/linux-arm/linux-trusted-services.git"
 				CACHE STRING "Linux FF-A user space shim repository URL")
-		set(LINUX_FFA_USER_SHIM_REFSPEC "main"
+		set(LINUX_FFA_USER_SHIM_REFSPEC "v1.0.0"
 				CACHE STRING "Linux FF-A user space shim git refspec")
 
 		find_program(GIT_COMMAND "git")