mmc: renesas_sdhi: Use BITS_PER_LONG helper

Use the existing BITS_PER_LONG helper definition instead of calculating
this value.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20200302093534.9055-1-geert+renesas@glider.be


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>