arch/x86: Fix cpu_cpuid_extended_level() return type

`cpuid_eax()` returns an unsigned integer.

Change-Id: Iebb6501130bc9ae333d45ae9d2e10c918245a6d1
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33814
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/arch/x86/cpu_common.c

@@ -49,7 +49,7 @@ int cpu_have_cpuid(void)
 }
 #endif
 
-int cpu_cpuid_extended_level(void)
+unsigned int cpu_cpuid_extended_level(void)
 {
 	return cpuid_eax(0x80000000);
 }