package/bmx7: drop useless $(d)

This was overlooked in commit
8e065065777e2955f385ae51b14c9f284b83e477 ("package/bmx7: new package")

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/bmx7/bmx7.mk

@@ -11,7 +11,7 @@ BMX7_LICENSE_FILES = LICENSE
 BMX7_DEPENDENCIES = zlib mbedtls wireless_tools
 
 define BMX7_BUILD_CMDS
-	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D)/$(d)/src
+	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D)/src
 endef
 
 define BMX7_INSTALL_TARGET_CMDS