scripts: Fix compilation warning. ...

Fix following warning:
scripts/kallsyms.c: In function ‘read_symbol’:
scripts/kallsyms.c:81:9: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result

Solution overtaken from kernel tree.

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

add kallsyms.c from linux kernel