usb: ci_udc: don't memalign() struct ci_req allocations

struct ci_req is a purely software structure, and needs no specific
memory alignment. Hence, allocate it with calloc() rather than
memalign(). The use of memalign() was left-over from when struct ci_req
was going to hold the aligned bounce buffer, but this is now dynamically
allocated.

Signed-off-by: Stephen Warren <swarren@nvidia.com>