apparmor: fix blob compression build failure on ppc

apparmor: fix blob compression build failure on ppc

security/apparmor/policy_unpack.c: In function 'deflate_compress':
security/apparmor/policy_unpack.c:1064:4: error: implicit declaration of function 'vfree'; did you mean 'kfree'? [-Werror=implicit-function-declaration]
    vfree(stgbuf);
    ^~~~~
    kfree

Fixes: 876dd866c084 ("apparmor: Initial implementation of raw policy blob compression")
Signed-off-by: John Johansen <john.johansen@canonical.com>