rust: miscdevice: remove unnecessary import
`kernel::str::CStr` is included in the prelude.
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250704-cstr-include-miscdevice-v1-1-bb9e9b17c892@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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