tests: Add sensor HTS221 to driver/build-all test case.

Change-Id: Ifd5acf8bfaa75a44458b448001c0f2335fd6364d
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>

tests/drivers/build_all/sensors_a_m.conf

diff --git a/tests/drivers/build_all/sensors_a_m.conf b/tests/drivers/build_all/sensors_a_m.conf
index 5ced100..5737f19 100644
--- a/tests/drivers/build_all/sensors_a_m.conf
+++ b/tests/drivers/build_all/sensors_a_m.conf
@@ -12,6 +12,7 @@
 CONFIG_DHT=y
 CONFIG_HDC1008=y
 CONFIG_HMC5883L=y
+CONFIG_HTS221=y
 #CONFIG_HP206C=y
 CONFIG_ISL29035=y
 CONFIG_LIS3DH=y