Fixes the following sparse warning:

drivers/mfd/twl6040.c:89:20: warning:
 symbol 'twl6040_patch' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NLee Jones <lee.jones@linaro.org>