ir: fix ir memory overflow issue

ir: fix ir memory overflow issue

PD#164774: kernel panic after mtk_cfg80211_set_power_mgmt

two possible overflow cases:
1. dev->debug_current + len == dev->debug_buffer_size
2. len > dev->debug_buffer_size

for the first case(currently triggered case)
  the last byte of string pointed to by fmt, aka.'\0', will
overwrite the first byte of memory pointed to by header(in
function __register_sysctl_table), which is just the LSB of
ipv4_table[]'s base address. Leading to "Unable to handle
kernel paging request at virtual address xxxx" panic

for the second case
  a bunch of memory pointed to by header(in function
__register_sysctl_table) will be overwritten

Change-Id: I6bc42308323b7ffb52fe4d1fa9d22742a31e8b1f
Signed-off-by: jiamin ma <jiamin.ma@amlogic.com>