pointers in ab8500-debugfs

Partly for coding style reasons, but mostly because sparse warns on it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Mattias Wallin <mattias.wallin@stericsson.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
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