soc: qcom: pil: Handle uninitialized 'ret'

The commit <a0a9abc9> (pil: Fix minidump collection during
SSR) failed to set the value of 'ret' in pil_do_minidump() upon
the return failure from prepare_minidump_segments(). As a result,
the 'goto seg_mapping_fail' will end up returning uninitialized
value. Hence, assign an error code explicitly to avoid this situation.

Change-Id: I20f0d2c4fd006483c73541937025ed50b265e2b4
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>