spi: sh-msiof: Use readl_poll_timeout_atomic() instead of open-coding

Replace the open-coded loop in sh_msiof_modify_ctr_wait() by a call to
the readl_poll_timeout_atomic() helper macro.

Suggested-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Mark Brown <broonie@kernel.org>