kconfig: some small fixes

- fix a typo in documentation
- fix a typo in a printk on error
- fix comments in dialog_inputbox()

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index c412c24..b472e4e 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -181,7 +181,7 @@
 (7) Returns the result of max(/expr/, /expr/).
 
 An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
-respectively for calculations). A menu entry becomes visible when it's
+respectively for calculations). A menu entry becomes visible when its
 expression evaluates to 'm' or 'y'.
 
 There are two types of symbols: constant and non-constant symbols.