[NFC][AsmPrinter] Pass MJTI by const reference instead of const pointer

[mingmingl-llvm]

The caller AsmPrinter::emitJumpTableInfo checks [1] MJTI is not a null pointer before calling emitJumpTableEntry or emitJumpTableSizesSection.

This patch updates callee function's signature to accept const reference, this way it's explicit MJTI won't be nullptr inside the callee.

[1]

llvm-project/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

Line 2857 in 9d5299e

if (!MJTI) return;

[snehasish]

lgtm