staging: speakup: fix misuse of kstrtol() in handle_goto()
A string of goto_buf has a number followed by x or y.
e.g. "3x" means move 3 lines down.
The kstrtol() returns an error(-EINVAL) with this string so
go_pos has unsigned a value of that error.
And also "*cp" has not expected value.
And fix sparse warnings:
drivers/staging/speakup/main.c:1901 handle_goto() warn: unsigned '(speakup_console[vc->vc_num]->go_pos)' is never less than zero.
drivers/staging/speakup/main.c:1911 handle_goto() warn: unsigned '(speakup_console[vc->vc_num]->go_pos)' is never less than zero.