check return value of gsm48_multirate_config()

Check the return value of gsm48_multirate_config() in function
lchan_set_single_amr_mode(). This prevents an invalid AMR mode
from being configured for a logical channel.

Because the VTY parsier limits the AMR mode range to 0-7 this
is just a theoretical issue. However, this fact is beyond the
understanding of a static code analyzer, and the absence of
error handling was indeed setting a bad example.

Change-Id: I61153a44e8b7a38332bf38718397be9b339d5f25
Related: CID#188940
1 file changed