Fix use of BFPR register in ether82563 driver.

It fixes support of the Intel 82579LM ethernet controller.
See Intel 6 Series Chipset Datasheet, § 21.1.1.
I also checked it still worked properly on Intel 82574L.

It should probably be tested on a wider range of Intel
ethernet controllers, notably Intel 82579V.

Reference: /n/sources/patch/applied/ether82563-bfpr
Date: Fri Apr 12 21:15:52 CES 2013
Signed-off-by: djc@9grid.fr

--- /sys/src/9/pc/ether82563.c	Thu Apr 11 23:55:03 2013
+++ /sys/src/9/pc/ether82563.c	Thu Apr 11 23:54:55 2013
@@ -388,7 +388,8 @@
 typedef struct {
 	u16int	*reg;
 	u32int	*reg32;
-	int	sz;
+	u16int	base;
+	u16int	lim;
 } Flash;
 
 enum {
@@ -1526,11 +1527,11 @@
 	if(f.reg == nil)
 		return -1;
 	f.reg32 = (void*)f.reg;
-	f.sz = f.reg32[Bfpr];
-	r = f.sz & 0x1fff;
+	f.base = f.reg32[Bfpr] & 0x1fff;
+	f.lim = f.reg32[Bfpr]>>16 & 0x1fff;
 	if(csr32r(c, Eec) & (1<<22))
-		r += c->type == i82579? 16 : 1;
-	r <<= 12;
+		f.base += f.lim+1 - f.base >> 1;
+	r = f.base << 12;
 
 	sum = 0;
 	for (adr = 0; adr < 0x40; adr++) {