regulator: tps65917/palmas: Simplify multiple dereference of ddata->palmas_matches[idx]

Converting dt to platform data logic involves picking up information
that is unique per regulator, however we can improve readability of
the code by dereferencing ddata->palmas_matches[idx] once in the loop.

While at it fix reuse of generic palmas_matches common variable
while reporting error for a specific regulator (which may be from
65917/palmas list).

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>