video: exynos_mipi_dsim: Remove unused variable

commit 7e0be9f9 ('video: exynos_mipi_dsim:
Use the generic PHY driver') resulted in a warning about an unused
variable:

drivers/video/exynos/exynos_mipi_dsi.c:144:26: warning: unused variable
    'pdev' [-Wunused-variable]

It is indeed unused; remove it.

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Inki Dae <inki.dae@samsung.com>