Android.mk: fix CFG_TEE_CLIENT_LOG_FILE checking
Android.mk: fix CFG_TEE_CLIENT_LOG_FILE checking

CFG_TEE_CLIENT_LOG_FILE variable contains the client library log file
path. The correct way to check if the variable is not empty is using
ifneq operator.

Signed-off-by: Ruslan Piasetskyi <ba54c793827dde3abc018a2b9acc315412c5814f@gmail.com>
Reviewed-by: Jens Wiklander <7706914404370d7502c27a0eff493dcf491feb51@linaro.org>

prime-zeng/optee_client