kconfig: Fix warning: ignoring return value of 'fwrite'

This fix facilitates fwrite() in both confdata.c and expr.c, either it
succeeds in writing, or an error occurs, or the end of file is reached.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/lkc.h

@@ -80,6 +80,13 @@ void sym_set_change_count(int count);
 void sym_add_change_count(int count);
 void conf_set_all_new_symbols(enum conf_def_mode mode);
 
+/* confdata.c and expr.c */
+static inline void xfwrite(const void *str, size_t len, size_t count, FILE *out)
+{
+	if (fwrite(str, len, count, out) < count)
+		fprintf(stderr, "\nError in writing or end of file.\n");
+}
+
 /* kconfig_load.c */
 void kconfig_load(void);