ASoC: pxa: fix null-pointer dereference in filter()

kasprintf() would return NULL pointer when kmalloc() fail to allocate.
Need to check the return pointer before calling strcmp().

Fixes: 7a824e21 ("ASoC: mmp: add audio dma support")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Link: https://lore.kernel.org/r/20221114085629.1910435-1-zengheng4@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>