Fixes gcc '-Wunused-but-set-variable' warning:[...]
drivers/ata/acard-ahci.c: In function acard_ahci_qc_prep:
drivers/ata/acard-ahci.c:268:15: warning: variable n_elem set but not
used [-Wunused-but-set-variable]
It is never used so can be removed. acard_ahci_fill_sg() is called only
in one place, use 'void' instead of 'int'.
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Hongbo Yao <yaohongbo@xxxxxxxxxx>