ENGR00174399 ASRC: fix mmap fail bug

ENGR00174399 ASRC: fix mmap fail bug

If output sample rate is less than input sample rate, it is possible
that the address of output dma buffer 0 can not be divided by page size.
Thus the mmap of output dma in the user space would fail and test
would fail.

let all output dma buffers allocate dma buffer together and we can
assure that the address of output dma buffer 0 can be divided by
page size.

Signed-off-by: Chen Liangjun <b36089@freescale.com>