MIR Parser: Extract the parsing of the operand's offset into a new method. NFC.
MIR Parser: Extract the parsing of the operand's offset into a new method. NFC.

This commit extract the code that parses the 64-bit offset from the method
'parseOperandsOffset' to a new method 'parseOffset' so that we can reuse it
when parsing the offset for the machine memory operands.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@244355 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm