sbc: fix license

sbc: fix license

sbc library itself is licensed under LGPLv2.1 or higher as mentioned in
sbc/sbc.h or any other file in sbc directory.

sbc test applications are licensed under GPLv2 or higher as mentioned in
src/sbcenc.c or any other file in src directory

Reported-by: Vladimir Koutny <vladimir.koutny@streamunlimited.com>
Signed-off-by: Radek Dostál <radek.dostal@streamunlimited.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Armin Kuster <akuster@mvista.com>