fsl/sata: correctly identify failed malloc

After allocating sata->cmd_hdr_tbl_offset we have to check
this variable and not variable sata.

The problem was indicated by cppcheck.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>

drivers/block/fsl_sata.c

@@ -124,7 +124,7 @@ int init_sata(int dev)
 	length = sizeof(struct cmd_hdr_tbl);
 	align = SATA_HC_CMD_HDR_TBL_ALIGN;
 	sata->cmd_hdr_tbl_offset = (void *)malloc(length + align);
-	if (!sata) {
+	if (!sata->cmd_hdr_tbl_offset) {
 		printf("alloc the command header failed\n\r");
 		return -1;
 	}