staging: fbtft: fix unchecked write return value in fb_agm1264k-fl

staging: fbtft: fix unchecked write return value in fb_agm1264k-fl

The second call to par->fbtftops.write() does not capture the return
value, so the subsequent error check tests a stale value from the
first write call. Add the missing assignment so the error check
applies to the correct write operation.

Signed-off-by: Artem Lytkin <iprintercanon@gmail.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Link: https://patch.msgid.link/20260207220523.3816-1-iprintercanon@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>