package/mesa3d: fix gallium-xa configure option

Fixes build warning:

output/build/mesa3d-20.3.2/meson.build:727: WARNING:
 gallium-xa option "false" deprecated, please use "disabled" instead.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/mesa3d/mesa3d.mk

@@ -74,7 +74,7 @@ endif
 else
 MESA3D_CONF_OPTS += \
 	-Dglx=disabled \
-	-Dgallium-xa=false
+	-Dgallium-xa=disabled
 endif
 
 ifeq ($(BR2_ARM_CPU_HAS_NEON),y)