loader: fix loading of kernels with . in path

The loader indended to search the kernel file name (only) for . but
instead searched the entire path, so paths like
"boot/test.elfv2/kernel" would not work.

Submitted by:	alfredo.junior_eldorado.org.br
Reviewed by:	kevans
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D19658

stand/common/load_elf.c

@@ -868,14 +868,16 @@ fake_modname(const char *name)
 		sp++;
 	else
 		sp = name;
-	ep = strrchr(name, '.');
-	if (ep) {
-		if (ep == name) {
-			sp = invalid_name;
-			ep = invalid_name + sizeof(invalid_name) - 1;
-		}
-	} else
-		ep = name + strlen(name);
+
+	ep = strrchr(sp, '.');
+	if (ep == NULL) {
+		ep = sp + strlen(sp);
+	}
+	if (ep == sp) {
+		sp = invalid_name;
+		ep = invalid_name + sizeof(invalid_name) - 1;
+	}
+
 	len = ep - sp;
 	fp = malloc(len + 1);
 	if (fp == NULL)