abis: align e1 input init prototypes for stricter compilers
Change return types of e1inp_dahdi_init(), e1inp_e1d_init() and
e1inp_rs232_init() from void to int to match their implementations.
Required for stricter compilers (e.g. Emscripten) which reject
mismatched function prototypes.
Change-Id: I93cd079003abb5665f1995647cfa94dc8e901ed9
