mmc: atmel-mci: fix mismatched section on atmci_cleanup_slot

As of 528bc780 ("mmc: atmel-mci: Release mmc resources on failure in probe"),
the atmci_probe() function calls atmci_cleanup_slot in the failure path.

This causes a new warning whenever the driver is built:

WARNING: drivers/mmc/host/built-in.o(.init.text+0xa04): Section mismatch in reference from the function atmci_probe() to the function .exit.text:atmci_cleanup_slot()
The function __init atmci_probe() references
a function __exit atmci_cleanup_slot().

Gcc correctly warns about this function getting dropped in the link stage
for the built-in case, which would cause undefined behavior when this error
path is hit. The solution is to simply drop the __exit annotation.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 528bc780 ("mmc: atmel-mci: Release mmc resources on failure in probe")
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>