input: synaptics_fw_update: Remove hardcoded firmware image name

Firmware name should be passed in based on target, not hardcoded.
Remove hardcoding and add appropriate error checking for this.

Change-Id: Ia95bf2abf8a86adc649d64d757f22d84c8e0053f
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>