phy: dphy: Correct lpx parameter and its derivatives(ta_{get,go,sure})

According to the comment of the function phy_mipi_dphy_get_default_config(),
it uses minimum D-PHY timings based on MIPI D-PHY specification.  They are
derived from the valid ranges specified in Section 6.9, Table 14, Page 41
of the D-PHY specification (v1.2).  The table 14 explicitly mentions that
the minimum T-LPX parameter is 50 nanoseconds and the minimum TA-SURE
parameter is T-LPX nanoseconds.  Likewise, the kernel doc of the 'lpx' and
'ta_sure' members of struct phy_configure_opts_mipi_dphy mentions that
the minimum values are 50000 picoseconds and @lpx picoseconds respectively.
Also, the function phy_mipi_dphy_config_validate() checks if cfg->lpx is
less than 50000 picoseconds and if cfg->ta_sure is less than cfg->lpx,
which hints the same minimum values.

Without this patch, the function phy_mipi_dphy_get_default_config()
wrongly sets cfg->lpx to 60000 picoseconds and cfg->ta_sure to 2 * cfg->lpx.
So, let's correct them to 50000 picoseconds and cfg->lpx respectively.

Note that I've only tested the patch with RM67191 DSI panel on i.MX8mq EVK.
Help is needed to test with other i.MX8mq, Meson and Rockchip platforms,
as I don't have the hardwares.

Fixes: dddc97e8

 ("phy: dphy: Add configuration helpers")
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Link: https://lore.kernel.org/r/20220216071257.1647703-1-victor.liu@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>