net: phy: Fix truncation of large IRQ numbers in phy_attached_print()

Given NR_IRQS is 2048 on sparc64, and even 32784 on alpha, 3 digits is
not enough to represent interrupt numbers on all architectures.  Hence
PHY interrupt numbers may be truncated during printing.

Increase the buffer size from 4 to 8 bytes to fix this.

Fixes: 5e369aef

 ("net: stmmac: Delete dead code for MDIO registration")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>