drm/amdgpu: Fix missing break in ATOM_ARG_IMM Case of atom_get_src_int()

Missing break statement in the ATOM_ARG_IMM case of a switch statement,
adds the missing break statement, ensuring that the program's control
flow is as intended.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/atom.c:323 atom_get_src_int() warn: ignoring unreachable code.

Fixes: d38ceaf9 ("drm/amdgpu: add core driver (v4)")
Cc: Jammy Zhou <Jammy.Zhou@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/atom.c

@@ -320,7 +320,7 @@ static uint32_t atom_get_src_int(atom_exec_context *ctx, uint8_t attr,
 				DEBUG("IMM 0x%02X\n", val);
 			return val;
 		}
-		return 0;
+		break;
 	case ATOM_ARG_PLL:
 		idx = U8(*ptr);
 		(*ptr)++;