staging: most: fix mbo leak

This patch fixes a potential MBO leak in case function aim_read()
exits right after the MBO has been fetched from kfifo and before
it has been saved to the variable stacked_mbo.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>