ARM: mach-shmobile: r8a7740: cleanup I2C workaround method

Current workaround of I2C on r8a7740 used mdelay(),
but it was an overkill.
This patch cleans up the workaround delay.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Simon Horman <horms@verge.net.au>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>