ASRock E350M1: mptable.c: Remove unused variable `dev`

When building the ASRock E350M1, the following warning is shown.

    $ make # on Jenkins (build server)
    […]
        CC         mainboard/asrock/e350m1/mptable.ramstage.o
    src/mainboard/asrock/e350m1/mptable.c:64:12: warning: unused variable 'dev' [-Wunused-variable]
    […]

Removing the variable `dev` addresses the warning.

The same change was done in the following commit for the
AMD Persimmon board.

    commit d7a696d0f2
    Author: efdesign98 <efdesign98@gmail.com>
    Date:   Thu Sep 15 15:24:26 2011 -0600

        Persimmon updates for AMD F14 rev C0

        Reviewed-on: http://review.coreboot.org/137

Change-Id: I83f4630cb6ab1e4c95d04b4e8423850ed1858e45
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: http://review.coreboot.org/2965
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/asrock/e350m1/mptable.c

@@ -62,7 +62,6 @@ static void *smp_write_config_table(void *v)
 
   /* I/O APICs:   APIC ID Version State   Address */
 
-  device_t dev;
   u32 dword;
   u8 byte;