net: phy: micrel: Correct bit assignments for phy_device flags

Previously, the defines for phy_device flags in the Micrel driver were
ambiguous in their representation. They were intended to be bit masks
but were mistakenly defined as bit positions. This led to the following
issues:

- MICREL_KSZ8_P1_ERRATA, designated for KSZ88xx switches, overlapped
  with MICREL_PHY_FXEN and MICREL_PHY_50MHZ_CLK.
- Due to this overlap, the code path for MICREL_PHY_FXEN, tailored for
  the KSZ8041 PHY, was not executed for KSZ88xx PHYs.
- Similarly, the code associated with MICREL_PHY_50MHZ_CLK wasn't
  triggered for KSZ88xx.

To rectify this, all three flags have now been explicitly converted to
use the `BIT()` macro, ensuring they are defined as bit masks and
preventing potential overlaps in the future.

Fixes: 49011e0c ("net: phy: micrel: ksz886x/ksz8081: add cabletest support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>