[media] rc-core: simplify sysfs code

Simplify and cleanup the sysfs code a bit.

[m.chehab@samsung.com: rebased and fixed a CodingStyle issue]
Signed-off-by: David Härdeman <david@hardeman.nu>

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>