qahw: test: link the math library for qahw_api

Add a option flag in the makefile under qahw_api/test
to link the math library for qahw_api's source files.

Change-Id: Iad699ad8c93c46b7e352bb25268992d72eaccee0
diff --git a/qahw_api/test/Makefile.am b/qahw_api/test/Makefile.am
index b4bbea7..851bf1c 100644
--- a/qahw_api/test/Makefile.am
+++ b/qahw_api/test/Makefile.am
@@ -39,4 +39,4 @@
 
 trans_loopback_test_CFLAGS  = $(CFLAGS) -Wno-sign-compare -Werror
 trans_loopback_test_CFLAGS  += $(trans_loopback_test_INCLUDES)
-trans_loopback_test_LDADD = -llog  -lutils ../libqahw.la -lcutils
+trans_loopback_test_LDADD = -llog  -lutils ../libqahw.la -lcutils -lm