phy: realtek: usb: Drop unnecessary error check for debugfs_create_dir()

Both debugfs_create_dir() and debugfs_create_file() return ERR_PTR
and never return NULL.

As Greg suggested, this patch removes the error checking for
debugfs_create_dir in phy-rtk-usb2.c and phy-rtk-usb3.c. This is because
the DebugFS kernel API is developed in a way that the caller can safely
ignore the errors that occur during the creation of DebugFS nodes. The
debugfs APIs have a IS_ERR() judge in start_creating() which can handle it
gracefully. So these checks are unnecessary.

Fixes: 134e6d25 ("phy: realtek: usb: Add driver for the Realtek SoC USB 2.0 PHY")
Fixes: adda6e82

 ("phy: realtek: usb: Add driver for the Realtek SoC USB 3.0 PHY")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230901075231.1368947-1-ruanjinjie@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>