xfs: Remove redundant assignment of mp

mp is being initialized to log->l_mp but this is never read
as record is overwritten later on. Remove the redundant
assignment.

Cleans up the following clang-analyzer warning:

fs/xfs/xfs_log_recover.c:3543:20: warning: Value stored to 'mp' during
its initialization is never read [clang-analyzer-deadcode.DeadStores].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>