[ProfileSummary] Standardize methods and fix comment

Every Analysis pass has a get method that returns a reference of the Result of
the Analysis, for example, BlockFrequencyInfo
&BlockFrequencyInfoWrapperPass::getBFI().  I believe that
ProfileSummaryInfo::getPSI() is the only exception to that, as it was returning
a pointer.

Another change is renaming isHotBB and isColdBB to isHotBlock and isColdBlock,
respectively.  Most methods use BB as the argument of variable names while
methods usually refer to Basic Blocks as Blocks, instead of BB.  For example,
Function::getEntryBlock, Loop:getExitBlock, etc.

I also fixed one of the comments.

Patch by Rodrigo Caetano Rocha!

Differential Revision: https://reviews.llvm.org/D54669

llvm-svn: 347182