ARM: dts: mdm9630: Switch the firmware name for the pil modem device

The MBA image is now loaded as part of the init_image op
when loading the modem. Thus peripheral-loader needs to
first load the primary modem image's headers instead of
the MBA headers. Switch the firmware name in the device
tree node.

Change-Id: I4e424c092120688263e2629875e17f63b8537381
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>