spi: bcm2835: bcm2835_spi_transfer_one_poll remove unnecessary argument

Remove the unnecessary argument of xfer_time_us when calling
bcm2835_spi_transfer_one_poll.

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>

Changelog:
  V1 -> V2: applied feedback by Stefan Wahren
            reorganized patchset
	    added extra rational, descriptions
Signed-off-by: Mark Brown <broonie@kernel.org>