staging: drm/omap: 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>