mm: cma: Print correct request pages

In case of cma allocation failure, req-size is logged, but instead of
requested size we are printing total size. Fix it.

Fixes: 45422bc8 ("mm: cma: Print region name on failure")
Change-Id: Ifc96209a0ccdb295fbb9767d3d93b3a567fa16fd
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>