staging: omap-thermal: Remove double conv_table reference

This patch removes from data structure the double reference of
the conversion table. It keeps the reference coming from bandgap
data definition. The patch also adapts the code accordingly.

Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>