hwclock: fix iopl implicit declaration warning on alpha

hwclock: fix iopl implicit declaration warning on alpha

Build warning:
sys-utils/hwclock-cmos.c: In function 'i386_iopl':
sys-utils/hwclock-cmos.c:611:9: warning: implicit declaration of function 'iopl' [-Wimplicit-function-declaration]
  return iopl(level);
         ^
sys-utils/hwclock-cmos.c:611:2: warning: nested extern declaration of 'iopl' [-Wnested-externs]
  return iopl(level);
  ^

Also:
checking sys/io.h usability... yes
checking sys/io.h presence... yes
checking for sys/io.h... yes

Full build log:
https://buildd.debian.org/status/fetch.php?pkg=util-linux&arch=alpha&ver=2.26.2-9&stamp=1440078034

Detected by/via:
https://qa.debian.org/bls/packages/u/util-linux.html

Please note that this has never been (build-)tested, but should hopefully
resolve the warning.

Signed-off-by: Andreas Henriksson <andreas@fatal.se>