hwclock: Remove ioperm declare as it causes nested extern declare warning

hwclock: Remove ioperm declare as it causes nested extern declare warning

The extern declaration causes the following warning:

```
  CC       sys-utils/hwclock-hwclock-cmos.o
sys-utils/hwclock-cmos.c: In function 'i386_iopl':
sys-utils/hwclock-cmos.c:356:20: warning: nested extern declaration of 'ioperm' [-Wnested-externs]
  356 |         extern int ioperm(unsigned long from, unsigned long num, int turn_on);
      |                    ^~~~~~
sys-utils/hwclock-cmos.c:356:20: warning: redundant redeclaration of 'ioperm' [-Wredundant-decls]
In file included from sys-utils/hwclock-cmos.c:68:
/usr/include/i386-gnu/sys/io.h:29:12: note: previous declaration of 'ioperm' with type 'int(long unsigned int,  long unsigned int,  int)'
   29 | extern int ioperm (unsigned long int __from, unsigned long int __num,
      |            ^~~~~~
  CCLD     hwclock
```