Remove obsolete comment about lack of locking for MMIO range lookup.

Pointed out by:	Tycho Nightingale (tycho.nightingale@plurisbusnetworks.com)
Need to call init_mem() to really initialize the MMIO range lookups.

This was working by accident because:
- the RB_HEADs were being initialized to zero as part of BSS
- the pthread_rwlock functions were implicitly initializing the lock object

Obtained from:	NetApp