[phantom] Remove unused variable in phantom_dmesg()

Reported-by: Ralph Giles <giles@thaumas.net>
Tested-by: Ralph Giles <giles@thaumas.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/phantom/phantom.c

 			    unsigned int max_lines ) {
 	uint32_t head;
 	uint32_t tail;
-	uint32_t len;
 	uint32_t sig;
 	uint32_t offset;
 	int byte;
 
 	/* Locate log */
 	head = phantom_readl ( phantom, UNM_CAM_RAM_DMESG_HEAD ( log ) );
-	len = phantom_readl ( phantom, UNM_CAM_RAM_DMESG_LEN ( log ) );
 	tail = phantom_readl ( phantom, UNM_CAM_RAM_DMESG_TAIL ( log ) );
 	sig = phantom_readl ( phantom, UNM_CAM_RAM_DMESG_SIG ( log ) );
 	DBGC ( phantom, "Phantom %p firmware dmesg buffer %d (%08x-%08x)\n",