sdspi no longer respects the sd spec startup sequence

[MabezDev]

https://github.com/MabezDev/embedded-fatfs/blob/46a39fd4dba9e5efe5931e0da67478475129ad13/sdspi/src/lib.rs#L101-L105

is no longer effective, because CS is managed by the SpiDevice, which means we cannot keep CS high while clocking out the 74 cycles.

I suppose we should remove this, and document that it needs to be done prior to sdspi's initialization.

cc: @CBJamo