[media] media: platform: sti: return -ENOMEM on errors

Function bdisp_debugfs_create() returns 0 even on errors. So its caller
cannot detect the errors. It may be better to return "-ENOMEM" on the
exception paths.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=188801

Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>