fixed linker error

[rolffokkens]

gcc 5.1.1 rightfully complains about this:
[rolf.fokkens@home07 bcache-tools-1.0.8.orig]$ make
cc -O2 -Wall -gpkg-config --cflags uuid blkid-c -o bcache.o bcache.c
bcache.c:125:9: warning: ‘crc_table’ is static but used in inline function ‘crc64’ which is not static
crc = crc_table[i] ^ (crc << 8);
^
cc -O2 -Wall -gpkg-config --cflags uuid blkidmake-bcache.c bcache.opkg-config --libs uuid blkid-o make-bcache
/tmp/cchVVBrJ.o: In functionwrite_sb': /tmp/bcache-tools-1.0.8.orig/make-bcache.c:277: undefined reference to crc64'
collect2: error: ld returned 1 exit status
<builtin>: recipe for target 'make-bcache' failed
make: *** [make-bcache] Error 1
[rolf.fokkens@home07 bcache-tools-1.0.8.orig]$