x86: fix "x86: use cpu_khz for loops_per_jiffy calculation"

fix:

arch/x86/kernel/tsc_32.c: In function ‘tsc_init':
arch/x86/kernel/tsc_32.c:421: error: ‘lpj_tsc' undeclared (first use in this function)
arch/x86/kernel/tsc_32.c:421: error: (Each undeclared identifier is reported only once
arch/x86/kernel/tsc_32.c:421: error: for each function it appears in.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>