boot/opensbi: update condition for custom tarball management

This patch updates the condition to handle custom tarballs as specified by
the configuration. This change is made to have cleaner condition and for
consistency.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

boot/opensbi/opensbi.mk

@@ -6,7 +6,7 @@
 
 OPENSBI_VERSION = $(call qstrip,$(BR2_TARGET_OPENSBI_VERSION))
 
-ifeq ($(OPENSBI_VERSION),custom)
+ifeq ($(BR2_TARGET_OPENSBI_CUSTOM_TARBALL),y)
 # Handle custom OpenSBI tarballs as specified by the configuration
 OPENSBI_TARBALL = $(call qstrip,$(BR2_TARGET_OPENSBI_CUSTOM_TARBALL_LOCATION))
 OPENSBI_SITE = $(patsubst %/,%,$(dir $(OPENSBI_TARBALL)))