Description: nfs: fix panic when nfs4_ff_layout_prepare_ds() fails
References:
Notes:
 carnil> Introduced in b739a5bd9d9f ("NFSv4/flexfiles: Cancel I/O if the layout is
 carnil> recalled or revoked"). Vulnerable versions: 6.1-rc1.
Bugs:
upstream: released (6.9-rc1) [719fcafe07c12646691bd62d7f8d94d657fa0766]
6.8-upstream-stable: released (6.8.2) [dac068f164ad05b35e7c0be13f138c3f6adca58f]
6.7-upstream-stable: released (6.7.11) [5ada9016b1217498fad876a3d5b07645cc955608]
6.6-upstream-stable: released (6.6.23) [7ca651b4ec4a049f5a46a0e5ff921b86b91c47c5]
6.1-upstream-stable: released (6.1.83) [31db25e3141b20e2a76a9f219eeca52e3cab126c]
5.10-upstream-stable: N/A "Vulnerable code not present"
4.19-upstream-stable: N/A "Vulnerable code not present"
sid: released (6.7.12-1)
6.1-bookworm-security: released (6.1.85-1)
5.10-bullseye-security: N/A "Vulnerable code not present"
4.19-buster-security: N/A "Vulnerable code not present"