gpio: virtuser: avoid non-constant format string

gpio: virtuser: avoid non-constant format string

Using a string variable as an sprintf format is potentially
dangerous, and gcc can warn about this:

drivers/gpio/gpio-virtuser.c: In function 'gpio_virtuser_dbgfs_init_line_attrs':
drivers/gpio/gpio-virtuser.c:808:9: error: format not a string literal and no format arguments [-Werror=format-security]
  808 |         sprintf(data->consumer, id);
      |         ^~~~~~~

Change it to a simpler strscpy() instead to just copy it and check
the destination buffer size.

Fixes: 91581c4b3f29 ("gpio: virtuser: new virtual testing driver for the GPIO API")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240719144422.2082394-1-arnd@kernel.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>