batman-adv: remove useless inline attribute for sysfs helper function

the compiler can optimize functions within the same C file and therefore
there is no need to make it explicit.

Remove the useless inline attribute for __batadv_store_uint_attr()

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>