vt: keyboard, Fix typo in the doc for vt_get_shift_state()

Kernel documentation validator is not happy:

.../keyboard.c:2195: warning: expecting prototype for vt_get_shiftstate(). Prototype was for vt_get_shift_state() instead

This is due to typo, fix it here.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210303083229.75784-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>