staging: sbe-2t3e3: use -ve error return codes in dc_init_descriptor_list

the dc_init_descriptor_list actually returns a +ve error return codes,
which is abnormal as other functions in kernel return -ve error codes on
failure. so replace the return codes of this function with -ve values
to make the consistency with the other functions in kernel.

Also make the dc_init_descriptor_list static as its never called
anywhere except in this file and move the function prototype from the
headerfile into the c file as its referred only in this c file.

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>