tty: sysrq: rename and re-type i in sysrq_handle_loglevel()

'i' is a too generic name for something which carries a 'loglevel'. Name
it as such and make it 'u8', the same as key will become in the next
patches.

Note that we are not stripping any high bits away, 'key' is given only
8bit values.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230712081811.29004-2-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>