Staging: speakup: fix an improperly-declared variable.

commit 4ea418b8b2fa8a70d0fcc8231b65e67b3a72984b upstream.

A local static variable was declared as a pointer to a string
constant.  We're assigning to the underlying memory, so it
needs to be an array instead.

Signed-off-by: Christopher Brannon <chris@the-brannons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>