libc2dcolorconvert: Update usage of kgsl_map_user_mem structure

Remove the use of reserve parameter.

Change-Id: Icae7830a52d8b589df54cb87e2cf0513772741b7
libc2dcolorconvert: clear kgsl param struct before calling MAP_USER_MEM

uinitialized struct members can fail mapping sporadically

Bug: 8764965 -- fix
Bug: 8329029 -- required
Change-Id: I594c2c51b4fed3403d419ad77a4d2ac919133ab2
Signed-off-by: Iliyan Malchev <malchev@google.com>