MIPS: ralink: Fix incorrect assignment on ralink_soc

ralink_soc sould be assigned to RT3883_SOC, replace incorrect
comparision with assignment.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Fixes: 418d29c8 ("MIPS: ralink: Unify SoC id handling")
Cc: John Crispin <john@phrozen.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14903/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/ralink/rt3883.c

@@ -157,5 +157,5 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 
 	rt2880_pinmux_data = rt3883_pinmux_data;
 
-	ralink_soc == RT3883_SOC;
+	ralink_soc = RT3883_SOC;
 }