MIPS: ralink: Fix invalid assignment of SoC type

BugLink: http://bugs.launchpad.net/bugs/1702863

commit 0af3a40f upstream.

Commit 418d29c8 ("MIPS: ralink: Unify SoC id handling") introduced
broken code. We obviously need to assign the value.
Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11993/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

arch/mips/ralink/rt288x.c

@@ -109,5 +109,5 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
 	soc_info->mem_size_max = RT2880_MEM_SIZE_MAX;
 
 	rt2880_pinmux_data = rt2880_pinmux_data_act;
-	ralink_soc == RT2880_SOC;
+	ralink_soc = RT2880_SOC;
 }