xtensa: fix variants path in the Kconfig help

The directory in the path should be "variants" instead of "variant".

Fixes: 420ae95 ("xtensa: simplify addition of new core variants")
Signed-off-by: Yujie Liu <yujie.liu@intel.com>
Message-Id: <20231129091337.2084747-1-yujie.liu@intel.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Author: Yujie-Liu

arch/xtensa/Kconfig

@@ -144,7 +144,7 @@ config XTENSA_VARIANT_CUSTOM_NAME
 	depends on XTENSA_VARIANT_CUSTOM
 	help
 	  Provide the name of a custom Xtensa processor variant.
-	  This CORENAME selects arch/xtensa/variant/CORENAME.
+	  This CORENAME selects arch/xtensa/variants/CORENAME.
 	  Don't forget you have to select MMU if you have one.
 
 config XTENSA_VARIANT_NAME