spi: atmel-quadspi: Free resources even if runtime resume failed in .remove()

In the Linux kernel, the following vulnerability has been resolved:

spi: atmel-quadspi: Free resources even if runtime resume failed in .remove()

An early error exit in atmel_qspi_remove() doesn't prevent the device
unbind. So this results in an spi controller with an unbound parent
and unmapped register space (because devm_ioremap_resource() is undone).
So using the remaining spi controller probably results in an oops.

Instead unregister the controller unconditionally and only skip hardware
access and clk disable.

Also add a warning about resume failing and return zero unconditionally.
The latter has the only effect to suppress a less helpful error message by
the spi core.