Fixes the following W=1 kernel build warning(s):
 drivers/gpu/drm/radeon/atombios_i2c.c:100:5: warning: no previous prototype for ‘radeon_atom_hw_i2c_xfer’ [-Wmissing-prototypes]
 100 | int radeon_atom_hw_i2c_xfer(struct i2c_adapter *i2c_adap,
 | ^~~~~~~~~~~~~~~~~~~~~~~
 drivers/gpu/drm/radeon/atombios_i2c.c:150:5: warning: no previous prototype for ‘radeon_atom_hw_i2c_func’ [-Wmissing-prototypes]
 150 | u32 radeon_atom_hw_i2c_func(struct i2c_adapter *adap)
 | ^~~~~~~~~~~~~~~~~~~~~~~
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
 bool atom_parse_cmd_header(struct atom_context *ctx, int index,
                           uint8_t *frev, uint8_t *crev);
 int atom_allocate_fb_scratch(struct atom_context *ctx);
+
+struct i2c_msg;
+struct i2c_adapter;
+int radeon_atom_hw_i2c_xfer(struct i2c_adapter *i2c_adap,
+                           struct i2c_msg *msgs, int num);
+u32 radeon_atom_hw_i2c_func(struct i2c_adapter *adap);
+
 #include "atom-types.h"
 #include "atombios.h"
 #include "ObjectID.h"
 
 #include "radeon.h"
 #include "atom.h"
 
-extern int radeon_atom_hw_i2c_xfer(struct i2c_adapter *i2c_adap,
-                                  struct i2c_msg *msgs, int num);
-extern u32 radeon_atom_hw_i2c_func(struct i2c_adapter *adap);
-
 bool radeon_ddc_probe(struct radeon_connector *radeon_connector, bool use_aux)
 {
        u8 out = 0x0;