firmware: meson-sm: unmap out_base shmem in error path

firmware: meson-sm: unmap out_base shmem in error path

When SM driver was introduced in [1], the code flow did not require
to unmap out_base shmem in case of errors inside probe().
During [2], the additional error path appeared, which requires unmap.

Patch adds iounmap() missed.

Links:
[1] https://lore.kernel.org/linux-amlogic/1466339944-602-2-git-send-email-carlo@caione.org/
[2] https://lore.kernel.org/linux-amlogic/1532613556-5398-1-git-send-email-narmstrong@baylibre.com/

Fixes: 0789724f86a5 ("firmware: meson_sm: Add serial number sysfs entry")
Signed-off-by: Evgeny Bachinin <EABachinin@salutedevices.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20231108125604.162383-3-EABachinin@salutedevices.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>