media: i2c: adv7842: Replace mdelay() with msleep() and usleep_range() in adv7842_ddr_ram_test()

adv7842_ddr_ram_test() is never called in atomic context.
It only calls from:
adv7842_ddr_ram_test() <- adv7842_command_ram_test() <- adv7842_ioctl()

adv7842_ddr_ram_test() calls mdelay() to busily wait,
which is not necessary.
mdelay() can be replaced with msleep() and usleep_range().

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>