habanalabs: if map page fails don't try to unmap it

The original code tried to unmap a page that was not mapped as part of
the map page error path.

Signed-off-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>