fs_parse: mark fs_param_bad_value() as static

fs_parse: mark fs_param_bad_value() as static

We found the following warning when build kernel with W=1:

fs/fs_parser.c:192:5: warning: no previous prototype for `fs_param_bad_value' [-Wmissing-prototypes]
int fs_param_bad_value(struct p_log *log, struct fs_parameter *param)
     ^
CC      drivers/usb/gadget/udc/snps_udc_core.o

And no header file define a prototype for this function, so we should mark
it as static.

Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/1601293463-25763-1-git-send-email-luojiaxing@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>