spi_qsd: Fix for SPI crash while updating the message status

When transfer speed exceeds the maximum supported frequency,
cur_msg is not initialized, Thus accessing the same cause kernel
crash. This patch corrects this.

CRs-Fixed: 647032
Change-Id: Ic0487a6b8859040f57c085fdcd78093480e64d49
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>