spi: spi-rpc-if: Check return value of rpcif_sw_init()

rpcif_sw_init() can fail so make sure we check the return value
of it and on error exit rpcif_spi_probe() callback with error code.

Fixes: eb8d6d46 ("spi: add Renesas RPC-IF driver")
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211025205631.21151-4-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-rpc-if.c

@@ -139,7 +139,9 @@ static int rpcif_spi_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	rpc = spi_controller_get_devdata(ctlr);
-	rpcif_sw_init(rpc, parent);
+	error = rpcif_sw_init(rpc, parent);
+	if (error)
+		return error;
 
 	platform_set_drvdata(pdev, ctlr);