net/openpgm: fix build on non-x86
cpu.c:44:7: error: invalid output constraint '=a' in asm
44 | : "=a"(cpu_info[0]), "=D"(cpu_info[1]), "=c"(cpu_info[2]), "=d"(cpu_info[3]) | ^
cpu.c:56:16: error: invalid output constraint '=a' in asm
56 | "xgetbv" : "=a"(eax), "=d"(edx) : "c"(xcr)); | ^
2 errors generated.