tty: synclink_gt, drop unneeded forward declarations

[ Upstream commit b9b90fe655c0bd816847ac1bcbf179cfa2981ecb ]

Forward declarations make the code larger and rewrites harder. Harder as
they are often omitted from global changes. Remove forward declarations
which are not really needed, i.e. the definition of the function is
before its first use.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-39-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>