tty: synclink_gt: rename a conflicting function name

'set_signals()' in synclink_gt.c conflicts with an exported symbol
in arch/um/, so change set_signals() to set_gtsignals(). Keep
the function names similar by also changing get_signals() to
get_gtsignals().

../drivers/tty/synclink_gt.c:442:13: error: conflicting types for ‘set_signals’
 static void set_signals(struct slgt_info *info);
             ^~~~~~~~~~~
In file included from ../include/linux/irqflags.h:16:0,
                 from ../include/linux/spinlock.h:58,
                 from ../include/linux/mm_types.h:9,
                 from ../include/linux/buildid.h:5,
                 from ../include/linux/module.h:14,
                 from ../drivers/tty/synclink_gt.c:46:
../arch/um/include/asm/irqflags.h:6:5: note: previous declaration of ‘set_signals’ was here
 int set_signals(int enable);
     ^~~~~~~~~~~

Fixes: 705b6c7b

 ("[PATCH] new driver synclink_gt")
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210902003806.17054-1-rdunlap@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>