Revert "seq_buf: Avoid type mismatch for seq_buf_init"

This reverts commit d494ddcc which is
commit d9a9280a0d0ae51dc1d4142138b99242b7ec8ac6 upstream.

It breaks the abi definitions, and there's no real need for it at all
other than for "correctness", so revert the thing.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I20ccc2690eca2c16adf507d679fa5e0a6c746e1c