pluging: add missing of dependency syslog on teec

Adds missing dependency of plugins/syslog example on libteec header files
that are brought in by libteec. The issue was reported by compiler with
the below build error message:

/tmp/optee/optee_examples/plugins/syslog/syslog_plugin.c:8:10: fatal error: tee_plugin_method.h: No such file or directory
    8 | #include <tee_plugin_method.h>
      |          ^~~~~~~~~~~~~~~~~~~~~

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>

Author: etienne-lms

plugins/syslog/CMakeLists.txt

@@ -5,4 +5,6 @@ set (CMAKE_SHARED_LIBRARY_PREFIX "")
 
 add_library(${PROJECT_NAME} SHARED syslog_plugin.c)
 
+target_link_libraries (${PROJECT_NAME} PRIVATE teec)
+
 install (TARGETS ${PROJECT_NAME} DESTINATION ${CFG_TEE_PLUGIN_LOAD_PATH})