util: Define inline function as static inline

util: Define inline function as static inline

The gcc in Centos 6.10 complains with

  src/nvme/util.h:120: multiple definition of `nvme_feature_decode_arbitration'

'inline' alone does not guarantee that the function gets inlined. The
compiler is still free to decide, thus in this case it doesn't inline
and that's why we having multiple implementation with the same
name (in different compile units). 'static inline' forces the inline
which was the indent of this code.

Signed-off-by: Daniel Wagner <dwagner@suse.de>