net: stmmac: dwmac4: fix PTP message type field extraction

net: stmmac: dwmac4: fix PTP message type field extraction

In dwmac4_wrback_get_rx_status(), the code extracts the PTP message
type from receive descriptor 1 using the dwmac enhanced descriptor
definitions:

	message_type = (rdes1 & ERDES4_MSG_TYPE_MASK) >> 8;

This is defined as:

 #define ERDES4_MSG_TYPE_MASK            GENMASK(11, 8)

The correct definition is RDES1_PTP_MSG_TYPE_MASK, which is also
defined as:

 #define RDES1_PTP_MSG_TYPE_MASK         GENMASK(11, 8)

Use the correct definition, converting to use FIELD_GET() to extract
it without needing an open-coded shift right that is dependent on the
mask definition.

As this change has no effect on the generated code, there is no need
to treat this as a bug fix.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vdtvn-00000002GtV-1wCS@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>