kerndat:fix compile err

Update to commit 78b8abe9
I find a compile err:

kerndat.c: In function 'kerndat_get_dirty_track':
kerndat.c:78:6: error: ignoring return value of 'read', declared with attribute warn_unused_result [-Werror=unused-result]
cc1: all warnings being treated as errors
make[2]: *** [kerndat.o] Error 1
make[1]: *** [built-in.o] Error 2
make[1]: Leaving directory `/home/clb/crtools'
make: *** [all] Error 2

Signed-off-by: Libo Chen <libo.chen@huawei.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>