CRED: Wrap task credential accesses in the FAT filesystem

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/fat/file.c b/fs/fat/file.c
index ddde370..81e2032 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -302,7 +302,7 @@
 {
 	mode_t allow_utime = sbi->options.allow_utime;
 
-	if (current->fsuid != inode->i_uid) {
+	if (current_fsuid() != inode->i_uid) {
 		if (in_group_p(inode->i_gid))
 			allow_utime >>= 3;
 		if (allow_utime & MAY_WRITE)