x86/mtrr: Remove unused variable

Compiling the kernel with W=1 results in the following warning:

arch/x86/kernel/cpu/mtrr/cleanup.c:299:16: warning: variable ‘second_basek’ set but not used [-Wunused-but-set-variable]
  unsigned long second_basek, second_sizek;

Remove the unused variable.

[ tglx: Massaged changelog ]

Signed-off-by: Bo Yu <tsu.yubo@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: puwen@hygon.cn
Link: https://lkml.kernel.org/r/20190208125343.11451-1-tsu.yubo@gmail.com