spi: use 'time_left' instead of 'timeout' with

Merge series from Wolfram Sang <wsa+renesas@sang-engineering.com>:

There is a confusing pattern in the kernel to use a variable named 'timeout' to
store the result of wait_for_*() functions causing patterns like:

        timeout = wait_for_completion_timeout(...)
        if (!timeout) return -ETIMEDOUT;

with all kinds of permutations. Use 'time_left' as a variable to make the code
obvious and self explaining.

This is part of a tree-wide series. The rest of the patches can be found here
(some parts may still be WIP):

git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux.git i2c/time_left

Because these patches are generated, I audit them before sending. This is why I
will send series step by step. Build bot is happy with these patches, though.
No functional changes intended.