arm: stm32mp: cleanup test on eth_env_set_enetaddr result

Remove the unnecessary inversion on the eth_env_set_enetaddr() result which
only make complex the code of setup_mac_address() and display an invalid
value in the associated pr_err.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Marek Vasut <marex@denx.de>

arch/arm/mach-stm32mp/cpu.c

@@ -580,8 +580,8 @@ __weak int setup_mac_address(void)
 		return -EINVAL;
 	}
 	pr_debug("OTP MAC address = %pM\n", enetaddr);
-	ret = !eth_env_set_enetaddr("ethaddr", enetaddr);
-	if (!ret)
+	ret = eth_env_set_enetaddr("ethaddr", enetaddr);
+	if (ret)
 		pr_err("Failed to set mac address %pM from OTP: %d\n",
 		       enetaddr, ret);
 #endif