parport: parport_pc: Mark expected switch fall-through

[ Upstream commit aa1f0fa374ed23528b915a693a11b0f275a299c0 ]

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 114730 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: ab11dac93d2d ("dev/parport: fix the array out-of-bounds risk")
Signed-off-by: Sasha Levin <sashal@kernel.org>