Build: Fix build error when Crypto Partition is disabled

This patch fixes build error when Crypto Partition is not enabled,
for example for Musca-B1 with -DFORWARD_PROT_MSG=1 build option.

This patch also replaces CMAKE_SOURCE_DIR with CMAKE_CURRENT_SOURCE_DIR
to have shorter and more stable paths.

Change-Id: I652afe9e48fc8d2391523cd7e835b4617a08515a
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
1 file changed