x86/alternatives: Mark text_poke_loc_init() static

The function is only used in this file so make it static.

 [ bp: Massage. ]

Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/1583253732-18988-1-git-send-email-hqjagain@gmail.com