bcache: fix sparse non static symbol warning
bcache: fix sparse non static symbol warning

Fixes the following sparse warning:

drivers/md/bcache/btree.c:2220:5: warning:
 symbol 'btree_insert_fn' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <b8f9cab8be13de37b9588aedad10a20fc3a68783@trendmicro.com.cn>
Signed-off-by: Kent Overstreet <99dffa8a9668ab7f6cde1c94b42a210109971113@daterainc.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs