phy: zynqmp: fix L0_TM_DISABLE_SCRAMBLE_ENCODER mask

phy: zynqmp: fix L0_TM_DISABLE_SCRAMBLE_ENCODER mask

The L0_TX_DIG_61 register bit 2 is a reserved read-only field.
The previous mask value 0x0f incorrectly included bit 2, causing
unintended writes to a reserved bit on every scrambler bypass
operation.

Correct the mask to (BIT(3) | GENMASK(1, 0)) to cover only the
valid scramble bypass control bits.

Fixes: 4a33bea00314 ("phy: zynqmp: Add PHY driver for the Xilinx ZynqMP Gigabit Transceiver")
Cc: stable@vger.kernel.org
Signed-off-by: Nava kishore Manne <nava.kishore.manne@amd.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Acked-by: Michal Simek <michal.simek@amd.com>
Link: https://patch.msgid.link/20260627155229.2791113-2-radhey.shyam.pandey@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>