net: stmmac: make variable data a u32

net: stmmac: make variable data a u32

Make data a u32 instead of an unsigned long, this way it is
explicitly the same width as the operations performed on it
and the same width as a writel store, and it cleans up sign
extention warnings when 64 bit static analysis is performed
on the code.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20250811111211.1646600-1-colin.i.king@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>