V4L/DVB (7610): em28xx: Select reg wait time based on chip ID

This is more conservative than just removing the msleep() from
em28xx_write_regs_req(), since some old hardware may still need it.
So, it will remove the sleep time only for those chips where this
removal were tested.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>