ASoC: Fix Blackfin I2S _pointer() implementation return in bounds values

ASoC: Fix Blackfin I2S _pointer() implementation return in bounds values

commit e999dc50404d401150a5429b6459473a691fd1a0 upstream.

The Blackfin DMA controller can report one frame beyond the end of the
buffer in the wraparound case but ALSA requires that the pointer always
be in the buffer. Do the wraparound to handle this. A similar bug is
likely to apply to the other Blackfin PCM drivers but the code is less
obvious to inspection and I don't have a user to test.

Reported-by: Kieran O'Leary <Kieran.O'Leary@wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>