soc/rockchip/rk3399/sdram: Simplify error condition

There is no need for explicit 0 comparison, any return value not equal
to 0 is treated as error.

Change-Id: I72612af4108a616b6247ee68c8ac2a53242b0853
Signed-off-by: Moritz Fischer <moritzf@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51126
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/soc/rockchip/rk3399/sdram.c

@@ -1133,7 +1133,7 @@ void sdram_init(const struct rk3399_sdram_params *params)
 		 * step may fail, before that, we just reset the
 		 * system, and start again.
 		 */
-		if (pctl_cfg(channel, params) != 0) {
+		if (pctl_cfg(channel, params)) {
 			printk(BIOS_ERR, "pctl_cfg fail, reset\n");
 			board_reset();
 		}