copybit: Fix compilation issues with -Werror

Fixes:
narrowing conversion of 'dst->copybit_image_t::w' from 'const uint32_t {aka const unsigned int}' to 'int' inside { } is ill-formed in C++11
narrowing conversion of 'dst->copybit_image_t::h' from 'const uint32_t {aka const unsigned int}' to 'int' inside { } is ill-formed in C++11
narrowing conversion of 'src->copybit_image_t::w' from 'const uint32_t {aka const unsigned int}' to 'int' inside { } is ill-formed in C++11
narrowing conversion of 'src->copybit_image_t::h' from 'const uint32_t {aka const unsigned int}' to 'int' inside { } is ill-formed in C++11
comparison between signed and unsigned integer expressions

Change-Id: I7b8d77e60a8fefd0b252fbe6c8863f576e8c6be2
Signed-off-by: bmc08gt <bmc08gt.teamb00sted@gmail.com>