x86: initialize io_bitmap_base on 32bit

commit db949bba3c7cf2e664ac12e237c6d4c914f0c69d (x86-32: use non-lazy
io bitmap context switching) broke ioperm for 32bit because it removed
the lazy initialization of io_bitmap_base and did not set it to the
real bitmap offset.

[ Impact: fix non-working sys_ioperm() on 32-bit kernels ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>