Input: ims-pcu - fix uninitialized use of 'error' in ims_pcu_buffers_alloc()

In case allocation via usb_alloc_coherent() fails in ims_pcu_buffers_alloc(),
the function jumps to the exit path without initializing local variable
'error' that is used as return value. Detected by Coverity - CID 1016531.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>