drm/amd/display: Fix nested FPU context in dcn21_validate_bandwidth()

Commit 41401ac6 added FPU wrappers to dcn21_validate_bandwidth(),
which was correct. Unfortunately a nested function alredy contained
DC_FP_START()/DC_FP_END() calls, which results in nested FPU context
enter/exit and complaints by kernel_fpu_begin_mask().
This can be observed e.g. with 5.10.20, which backported 41401ac6
and now emits the following warning on boot:

WARNING: CPU: 6 PID: 858 at arch/x86/kernel/fpu/core.c:129 kernel_fpu_begin_mask+0xa5/0xc0
Call Trace:
 dcn21_calculate_wm+0x47/0xa90 [amdgpu]
 dcn21_validate_bandwidth_fp+0x15d/0x2b0 [amdgpu]
 dcn21_validate_bandwidth+0x29/0x40 [amdgpu]
 dc_validate_global_state+0x3c7/0x4c0 [amdgpu]

The warning is emitted due to the additional DC_FP_START/END calls in
patch_bounding_box(), which is inlined into dcn21_calculate_wm(),
its only caller. Removing the calls brings the code in line with
dcn20 and makes the warning disappear.

Fixes: 41401ac6 ("drm/amd/display: Add FPU wrappers to dcn21_validate_bandwidth()")
Signed-off-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

@@ -1062,8 +1062,6 @@ static void patch_bounding_box(struct dc *dc, struct _vcs_dpi_soc_bounding_box_s
 {
 	int i;
 
-	DC_FP_START();
-
 	if (dc->bb_overrides.sr_exit_time_ns) {
 		for (i = 0; i < WM_SET_COUNT; i++) {
 			  dc->clk_mgr->bw_params->wm_table.entries[i].sr_exit_time_us =
@@ -1088,8 +1086,6 @@ static void patch_bounding_box(struct dc *dc, struct _vcs_dpi_soc_bounding_box_s
 				dc->bb_overrides.dram_clock_change_latency_ns / 1000.0;
 		}
 	}
-
-	DC_FP_END();
 }
 
 void dcn21_calculate_wm(