drm/imagination: vm: Fix heap lookup condition

When conditionally checking for heap existence of a certian address in
pvr_vm_bind_op_map_init the condition whether the map request comes from a
user is incorrect: The context must not be the kernel-context to be a
user(space) context and should be looked up in pvr_heaps.

That makes addresses coming from userspace not being verfied against the
defined ranges and prevents firmware loading for meta cores.

Fixes: ff5f643d ("drm/imagination: Add GEM and VM related code")
Signed-off-by: Alex Bee <knaerzche@gmail.com>
Reviewed-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231208170856.1748413-1-knaerzche@gmail.com