drm/sun4i: dsi: delete unnecessary IS_ERR() checks

The "dsi->bus_clk" pointer cannot be an error pointer at this point.
The check is confusing and unnecessary. Delete it.

Signed-off-by: Dan Carpenter <[e-mail]>
Signed-off-by: Maxime Ripard <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/YmqH71MtoGn2AXUg@kili

drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

···
 err_unprotect_clk:
 	clk_rate_exclusive_put(dsi->mod_clk);
 err_attach_clk:
-	if (!IS_ERR(dsi->bus_clk))
-		regmap_mmio_detach_clk(dsi->regs);
+	regmap_mmio_detach_clk(dsi->regs);
+
 	return ret;
 }
 
···
 	mipi_dsi_host_unregister(&dsi->host);
 	clk_rate_exclusive_put(dsi->mod_clk);
 
-	if (!IS_ERR(dsi->bus_clk))
-		regmap_mmio_detach_clk(dsi->regs);
+	regmap_mmio_detach_clk(dsi->regs);
 
 	return 0;
 }