ata: pata_legacy: fix pdc20230_set_piomode()

ata: pata_legacy: fix pdc20230_set_piomode()

[ Upstream commit 55a5095349df4fd229bdf58179374cc1bb0a732e ]

Clang gives a warning when compiling pata_legacy.c with 'make W=1' about
the 'rt' local variable in pdc20230_set_piomode() being set but unused.
Quite obviously, there is an outb() call missing to write back the updated
variable. Moreover, checking the docs by Petr Soucek revealed that bitwise
AND should have been done with a negated timing mask and the master/slave
timing masks were swapped while updating...

Fixes: 1f538e3509a8 ("[libata] Add a bunch of PATA drivers.")
Reported-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>