arm: Fix compilation error with gcc 4.5.2

Fix warning with the LDM/STM instructions. The instructions dont
have a register offset so set the offset to 0.

Change-Id: I2c988373c88e280015faa43076139650747d7ff3
Acked-by: Kaushik Sikdar <ksikdar@qualcomm.com>
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>