x-wic.inc: Use ROOT_PARTITION_SIZE to define A/B partition sizes

It's clearer to have one root partition size variable that is used in
the setup of both A and B partitions.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

meta-ohos-core/conf/distro/include/x-wic.inc

@@ -8,9 +8,10 @@
 
 BOOT_PARTITION_SIZE ?= "512M"
 # The SECO B68 board pulls in almost half a Gigabyte worth of linux-firmware.
-ROOTA_PARTITION_SIZE_seco-intel-b68 ?= "1536M"
-ROOTA_PARTITION_SIZE ?= "1G"
-ROOTB_PARTITION_SIZE ?= "${ROOTA_PARTITION_SIZE}"
+ROOT_PARTITION_SIZE_seco-intel-b68 ?= "1536M"
+ROOT_PARTITION_SIZE ?= "1G"
+ROOTA_PARTITION_SIZE = "${ROOT_PARTITION_SIZE}"
+ROOTB_PARTITION_SIZE = "${ROOT_PARTITION_SIZE}"
 DEVICEDATA_PARTITION_SIZE ?= "8M"
 SYSDATA_PARTITION_SIZE ?= "512M"
 APPDATA_PARTITION_SIZE ?= "1G"