Description: md: fix kmemleak of rdev->serial
References:
Notes:
 carnil> Introduced in 963c555e75b0 ("md: introduce mddev_create/destroy_wb_pool for the
 carnil> change of member device"). Vulnerable versions: 5.3-rc1.
Bugs:
upstream: released (6.9-rc1) [6cf350658736681b9d6b0b6e58c5c76b235bb4c4]
6.8-upstream-stable: released (6.8.2) [4c1021ce46fc2fb6115f7e79d353941e6dcad366]
6.7-upstream-stable: released (6.7.11) [6d32c832a88513f65c2c2c9c75954ee8b387adea]
6.6-upstream-stable: needed
6.1-upstream-stable: needed
5.10-upstream-stable: needed
4.19-upstream-stable: N/A "Vulnerable code not present"
sid: released (6.7.12-1)
6.1-bookworm-security: needed
5.10-bullseye-security: needed
4.19-buster-security: N/A "Vulnerable code not present"