spi: dw-mid: avoid potential NULL dereference
spi: dw-mid: avoid potential NULL dereference

When DMA descriptor allocation fails we should not try to assign any fields in
the bad descriptor. The patch adds the necessary checks for that.

Fixes: 7063c0d942a1 (spi/dw_spi: add DMA support)
Signed-off-by: Andy Shevchenko <74f0c009df510614346aa771cd21959b78cdb413@linux.intel.com>
Signed-off-by: Mark Brown <b51b9a92386687a9ac927cebfa0f978adeb8cea5@kernel.org>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs