init/Kconfig: rework help of CONFIG_CC_OPTIMIZE_FOR_SIZE

CONFIG_CC_OPTIMIZE_FOR_SIZE was originally an independent boolean
option, but commit 877417e6 ("Kbuild: change CC_OPTIMIZE_FOR_SIZE
definition") turned it into a choice between _PERFORMANCE and _SIZE.

The phrase "If unsure, say N." sounds like an independent option.
Reword the help text to make it appropriate for the choice menu.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

init/Kconfig

@@ -1219,10 +1219,8 @@ config CC_OPTIMIZE_FOR_SIZE
 	bool "Optimize for size"
 	imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED  # avoid false positives
 	help
-	  Enabling this option will pass "-Os" instead of "-O2" to
-	  your compiler resulting in a smaller kernel.
-
-	  If unsure, say N.
+	  Choosing this option will pass "-Os" to your compiler resulting
+	  in a smaller kernel.
 
 endchoice