drm/msm: Set proper GEM address space range for drm mm allocator

GEM address space range provided to drm mm allocator is not correct.
Start address and size of the address space should be passed to drm mm
initializer. Instead of size, end address of address space range is
passed to drm mm initializer.
msm_gem_get_iova() returns 0, even if memory mapping to virtual
address space is failed. Return proper error value to user space
driver incase of error.

Change-Id: I356a63b873094cb465909437dcdab9513e27b7ff
Signed-off-by: Venkateswara Rao Tadikonda <vtadik@codeaurora.org>