pkg-infra: put optional step_user def and assignment in one block

Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pkg-generic.mk

@@ -56,11 +56,11 @@ endef
 GLOBAL_INSTRUMENTATION_HOOKS += step_time
 
 # User-supplied script
+ifneq ($(BR2_INSTRUMENTATION_SCRIPTS),)
 define step_user
 	@$(foreach user_hook, $(BR2_INSTRUMENTATION_SCRIPTS), \
 		$(EXTRA_ENV) $(user_hook) "$(1)" "$(2)" "$(3)"$(sep))
 endef
-ifneq ($(BR2_INSTRUMENTATION_SCRIPTS),)
 GLOBAL_INSTRUMENTATION_HOOKS += step_user
 endif