CRED: fix build error due to 'tgcred' undeclared
CRED: fix build error due to 'tgcred' undeclared

This patch adds CONFIG_KEYS guard for tgcred to fix below build error
if CONFIG_KEYS is not configured.

  CC      kernel/cred.o
kernel/cred.c: In function 'prepare_kernel_cred':
kernel/cred.c:657: error: 'tgcred' undeclared (first use in this function)
kernel/cred.c:657: error: (Each undeclared identifier is reported only once
kernel/cred.c:657: error: for each function it appears in.)
make[1]: *** [kernel/cred.o] Error 1
make: *** [kernel] Error 2

Signed-off-by: Axel Lin <b6ffd6973e972cb999e8e535ab74da7fee0c035f@gmail.com>
Acked-by: David Howells <ebac1d06c1688626821bb0e574a037a7a5354e49@redhat.com>
Signed-off-by: James Morris <10d11de3abc355eabe955bb734f0f8e71da56e16@namei.org>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas