bus: mhi: host: Remove unused functions

bus: mhi: host: Remove unused functions

mhi_device_get() and mhi_queue_dma() haven't been used since 2020's
commit 189ff97cca53 ("bus: mhi: core: Add support for data transfer")
added them.

Remove them.

Note that mhi_queue_dma_sync() is used and has been left.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250127215859.261105-1-linux@treblig.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>