regmap: Rename ret variable in regmap_read_poll_timeout

As almost all of the callers of the regmap_read_poll_timeout macro
will include a local ret variable we will always get a Sparse warning
about the duplication of the ret variable:

warning: symbol 'ret' shadows an earlier one

Simply rename the ret variable in the marco to pollret to make this
significantly less likely to happen.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>