drm/msm/dsi: Remove set but not used variable 'lpx'

drm/msm/dsi: Remove set but not used variable 'lpx'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/msm/dsi/phy/dsi_phy.c: In function msm_dsi_dphy_timing_calc_v2:
drivers/gpu/drm/msm/dsi/phy/dsi_phy.c:156:17: warning: variable lpx set but not used [-Wunused-but-set-variable]
drivers/gpu/drm/msm/dsi/phy/dsi_phy.c: In function msm_dsi_dphy_timing_calc_v3:
drivers/gpu/drm/msm/dsi/phy/dsi_phy.c:273:17: warning: variable lpx set but not used [-Wunused-but-set-variable]

'lpx' in msm_dsi_dphy_timing_calc_v2 is not used since commit bd342882c49f
("drm/msm/dsi: Add new method to calculate 14nm PHY timings")

'lpx' in msm_dsi_dphy_timing_calc_v3 is not used since commit d93a8273bc66
("drm/msm/dsi: implement auto PHY timing calculator for 10nm PHY")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1570690506-83287-4-git-send-email-zhengbin13@huawei.com