wandboard: Fix the DM_PMIC conversion

wandboard: Fix the DM_PMIC conversion

Commit ec837c82d709 ("imx6: wandboard: convert to DM_PMIC")
caused the following pmic_get() error:

CPU:   Freescale i.MX6QP rev1.0 at 792 MHz
Reset cause: POR
DRAM:  2 GiB
PMIC:  pmic_get() ret -19
...

and since the PMIC presence is used to determine the board D1 revision,
the following error is seen when booting a board rev D1:

WARNING: Could not determine dtb to use

and the kernel does not boot at all.

Fix the regression by passing "pfuze100@8" as the correct parameter
to the pmic_get() function in the DM case.

Fixes: ec837c82d709 ("imx6: wandboard: convert to DM_PMIC")
Signed-off-by: Fabio Estevam <festevam@gmail.com>