debian/rules: Use DEB_BUILD_ARCH, rather than DEB_HOST_ARCH when detecting armhf build system.

debian/rules

@@ -6,8 +6,8 @@ include /usr/share/dpkg/buildflags.mk
 
 NULL =
 
-DEB_HOST_ARCH=$(shell dpkg-architecture -qDEB_HOST_ARCH)
-ifneq (,$(filter armhf,$(DEB_HOST_ARCH)))
+DEB_BUILD_ARCH=$(shell dpkg-architecture -qDEB_BUILD_ARCH)
+ifneq (,$(filter armhf,$(DEB_BUILD_ARCH)))
 ARM_FLOAT_ABI = -DARM_FP_ABI=hard
 else
 ARM_FLOAT_ABI =