exec/memory: Fix kernel-doc warning

exec/memory: Fix kernel-doc warning

During build the kernel-doc script complains about the following issue:

  src/docs/../include/exec/memory.h:1741: warning: Function parameter or member 'n' not described in 'memory_region_unmap_iommu_notifier_range'
  src/docs/../include/exec/memory.h:1741: warning: Excess function parameter 'notifier' description in 'memory_region_unmap_iommu_notifier_range'

Settle on "notifier" for consistency with other memory functions.

Fixes: 7caebbf9ea53
       ("memory: introduce memory_region_unmap_iommu_notifier_range()")
Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230315072552.47117-1-shentey@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>