qcacld-3.0: Kconfig: Rename BUILD_TIMESTAMP

Change I66d159a1594f71fdf33f3e4b4e6be4840d7e140a ("qcacld-3.0: Include
change Ids in build tag") replaced the usage of CONFIG_BUILD_TIMESTAMP
with CONFIG_BUILD_TAG. However, that change did not actually modify
the Kconfig item, so do it now.

Change-Id: Id69a339a8d539b3cd5b455c411ae10652f6aa897
CRs-Fixed: 3487377

Kconfig

@@ -115,8 +115,8 @@ config ICMP_DISABLE_PS
 	bool "Enable ICMP packet disable powersave feature"
 	default n
 
-config BUILD_TIMESTAMP
-	bool "Embed timestamp in wlan version"
+config BUILD_TAG
+	bool "Embed tags and timestamp in wlan version"
 	default n
 
 config WLAN_FEATURE_FILS