radv: Fix uninitialized variable in renderpass.

Fixes some dEQP-VK.renderpass2.* flakes. Valgrind:

Test case 'dEQP-VK.renderpass2.dedicated_allocation.attachment.8.724'..
==754520== Conditional jump or move depends on uninitialised value(s)
==754520==    at 0x575B21C: radv_layout_is_htile_compressed (radv_image.c:1690)
==754520==    by 0x572F470: radv_handle_depth_image_transition (radv_cmd_buffer.c:5855)
==754520==    by 0x572F2F2: radv_handle_image_transition (radv_cmd_buffer.c:6123)
==754520==    by 0x572EEC6: radv_handle_subpass_image_transition (radv_cmd_buffer.c:3385)
==754520==    by 0x572A104: radv_cmd_buffer_begin_subpass (radv_cmd_buffer.c:4843)
==754520==    by 0x572A007: radv_CmdBeginRenderPass (radv_cmd_buffer.c:4913)
==754520==    by 0x572A197: radv_CmdBeginRenderPass2 (radv_cmd_buffer.c:4921)

Why false?

A renderloop happens when the same attachment is both used as input attachment and output (color, ds) attachment in a subpass. Of course this doesn't happen outside of a renderpass and hence we can initialize it to false at the start of the renderpass.

Fixes: 66131ceb "radv: Pass through render loop detection to internal layout decisions."