clang warns:

drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:995:39: warning:
implicit conversion from enumeration type 'PPCLK_e' to different
enumeration type 'enum smu_clk_type' [-Wenum-conversion]
                ret = smu_get_current_clk_freq(smu, PPCLK_SOCCLK, &now);
                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:1016:39: warning:
implicit conversion from enumeration type 'PPCLK_e' to different
enumeration type 'enum smu_clk_type' [-Wenum-conversion]
                ret = smu_get_current_clk_freq(smu, PPCLK_FCLK, &now);
                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/vega20_ppt.c:1031:39: warning:
implicit conversion from enumeration type 'PPCLK_e' to different
enumeration type 'enum smu_clk_type' [-Wenum-conversion]
                ret = smu_get_current_clk_freq(smu, PPCLK_DCEFCLK, &now);
                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~

The values are mapped one to one in vega20_get_smu_clk_index so just use
the proper enums here.

Fixes: 09676101 ("drm/amd/powerplay: support sysfs to get socclk, fclk, dcefclk")
Link: https://github.com/ClangBuiltLinux/linux/issues/587Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>