base: genlock: Use a signed long for the result from wait_timeout

interruptible_wait_timeout returns a signed long, so make sure that
we use a signed long to hold the result. Using an unsigned value would
horribly misinterpet an error such as -ERESTARTSYS.

CRs-Fixed: 341347
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
(cherry picked from commit be669bc92358653a46c63f2352e6d981f9ed3bdf)

Change-Id: Ifcf555f8719f9c74fdb6d8b5cf2a32582988335b
Signed-off-by: Ram Kumar Chakravarthy Chebathini <rcheba@codeaurora.org>