net: phy: Fix signed shift overflow

Booting R-Car Gen3 arm64 U-Boot with CONFIG_UBSAN=y resulted in:

 =====================================================================
 UBSAN: Undefined behaviour in drivers/net/phy/phy.c:728:19
 left shift of 1 by 31 places cannot be represented in type 'int'
 =====================================================================

Fix it by appending the UL suffix to the numeric literal. While at it,
convert the type of "addr" variable from signed to unsigned, to protect
against shifting the numeric literal by a negative value (which would
lead to yet another undefined behavior).

Fixes: 1adb406b ("phy: add phy_find_by_mask/phy_connect_dev")
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>

* Using U-suffix for integer is sufficient.
* ffs() of non-zero value cannot be 0. But addr being unsigned is
* preferable.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>