MIR Serialization: Change syntax for the call entry pseudo source values.

MIR Serialization: Change syntax for the call entry pseudo source values.

The global IR values in machine memory operands should use the global value
'@<name>' syntax instead of the current '%ir.<name>' syntax.

However, the global value call entry pseudo source values use the global value
syntax already. Therefore, the syntax for the call entry pseudo source values
has to be changed so that the global values and call entry global value PSVs
can be parsed without ambiguities.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245526 91177308-0d34-0410-b5e6-96231b3b80d8