common: cmd pmic: command cleanup

This commit cleanups the use of function: failed().
The new function name is: failure(), and it is used
for print errno and the errno-related message only.

The second change is choosing PMIC device by it's name,
instead of seq number. Thanks to this change, for set
the current device, call of pmic_get() is enough.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested on sandbox:
Tested-by: Simon Glass <sjg@chromium.org>