spi: aspeed: Fix an error handling path in aspeed_spi_[read|write]_user()

A aspeed_spi_start_user() is not balanced by a corresponding
aspeed_spi_stop_user().
Add the missing call.

Fixes: e3228ed9 ("spi: spi-mem: Convert Aspeed SMC driver to spi-mem")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/4052aa2f9a9ea342fa6af83fa991b55ce5d5819e.1732051814.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Mark Brown <broonie@kernel.org>