ata: ahci_xgene: Use int type for 'rc' to store error codes

Use int instead of u32 for the 'rc' variable in xgene_ahci_softreset()
to store negative error codes returned by ahci_do_softreset().

In xgene_ahci_pmp_softreset(), remove the redundant 'rc' variable and
directly return the result of the ahci_do_softreset() call instead.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>