PM / OPP: Fix parsing of opp-microvolt and opp-microamp properties

Commit 01fb4d3c ("PM / OPP: Parse 'opp-<prop>-<name>'
bindings") broke support for parsing standard opp-microvolt and
opp-microamp properties.  Fix it by setting 'name' string to
proper value for !prop cases.

Fixes: 01fb4d3c ("PM / OPP: Parse 'opp-<prop>-<name> 'bindings")
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>