PM / OPP: Use ERR_CAST instead of ERR_PTR(PTR_ERR())

Use ERR_CAST inlined function instead of ERR_PTR(PTR_ERR(...))

[The semantic patch that makes this change is available
 in scripts/coccinelle/api/err_cast.cocci.

 More information about semantic patching is available at
 http://coccinelle.lip6.fr/]

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>