[ALSA] mpu401: reduce tx loop timeout

[ALSA] mpu401: reduce tx loop timeout

Reduce the number of times to check for a non-empty Tx FIFO from 100 to
2 because there is no MPU-401 implementation that needs more than one or
two reads to determine the actual FIFO status.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>