Fix spelling of unknown
Suppress annoying but harmless warning about unknown module

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[    4.237575] sd 2:0:0:0: [sda] Assuming drive cache: write through
[    4.239183] sd 2:0:0:0: [sda] Assuming drive cache: write through
[    4.524950] sd 2:0:0:0: [sda] Assuming drive cache: write through
modprobe: module unknown not found in modules.dep