btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

btrfs: avoid null pointer dereference on fs_info when calling btrfs_crit

[ Upstream commit 3993b112dac968612b0b213ed59cb30f50b0015b ]

There are checks on fs_info in __btrfs_panic to avoid dereferencing a
null fs_info, however, there is a call to btrfs_crit that may also
dereference a null fs_info. Fix this by adding a check to see if fs_info
is null and only print the s_id if fs_info is non-null.

Detected by CoverityScan CID#401973 ("Dereference after null check")

Fixes: efe120a067c8 ("Btrfs: convert printk to btrfs_ and fix BTRFS prefix")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>