spi: spi-altera-dfl: Fix an error handling path

The spi_alloc_master() call is not undone in all error handling paths.
Moreover, there is no .remove function to release the allocated memory.

In order to fix both this issues, switch to devm_spi_alloc_master().

This allows further simplification of the probe.

Fixes: ba2fc167

 ("spi: altera: Add DFL bus driver for Altera API Controller")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/0607bb59f4073f86abe5c585d35245aef0b045c6.1653805901.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Mark Brown <broonie@kernel.org>