ata: libahci: fix parameter type of ahci_exec_polled_cmd()

ahci_exec_polled_cmd() passes its 'unsigned long timeout_msec' parameter
to ata_wait_register() that now takes 'unsigned int' -- eliminate unneeded
implicit casts, not forgetting about ahci_do_softreset()...

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>