i2o: eliminate a peculiar constraint on i2o_max_drivers

There is no reason i2o_max_drivers must be a power of two.  This patch
eliminates such a constraint.

Cc: Markus Lidel <Markus.Lidel@shadowconnect.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>