PR16490: fix a crash in ARMDAGToDAGISel::SelectInlineAsm.

In the SelectionDAG immediate operands to inline asm are constructed as
two separate operands. The first is a constant of value InlineAsm::Kind_Imm
and the second is a constant with the value of the immediate.

In ARMDAGToDAGISel::SelectInlineAsm, if we reach an operand of Kind_Imm we
should skip over the next operand too.