accel/qaic: Synchronize access to DBC request queue head & tail pointer

Two threads of the same process can potential read and write parallelly to
head and tail pointers of the same DBC request queue. This could lead to a
race condition and corrupt the DBC request queue.

Fixes: ff13be83 ("accel/qaic: Add datapath")
Signed-off-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Signed-off-by: Youssef Samir <youssef.abdulrahman@oss.qualcomm.com>
Reviewed-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>
Reviewed-by: Carl Vanderlip <carl.vanderlip@oss.qualcomm.com>
[jhugo: Add fixes tag]
Signed-off-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20251007061837.206132-1-youssef.abdulrahman@oss.qualcomm.com