patch.bbclass: Move vardepsexclude flag to be along side the function using the variable

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

meta/classes/patch.bbclass

@@ -126,6 +126,7 @@ python patch_do_patch() {
 			raise bb.build.FuncFailed(str(sys.exc_value))
 		resolver.Resolve()
 }
+patch_do_patch[vardepsexclude] = "DATE SRCDATE"
 
 addtask patch after do_unpack
 do_patch[dirs] = "${WORKDIR}"