media: dvb-usb-v2/gl861: use usleep_range() for short delay

As the kernel doc "timers-howto.txt" reads,
short delay with msleep() can take much longer.
In a case of raspbery-pi platform where CONFIG_HZ_100 was set,
it actually affected the init of Friio devices
since it issues lots of i2c transactions with short delay.

Signed-off-by: Akihiro Tsukada <tskd08@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>