ALSA: line6: Add delay before reading status

The device indicates the result of a read/write operation by making the
status available on a subsequent request from the driver.  This is not
ready immediately, though, so the driver is currently slamming the
device with hundreds of pointless requests before getting the expected
response.  Add a two millisecond delay before each attempt.  This is
approximately the behavior observed with version 4.2.7.1 of the Windows
driver.

Signed-off-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>