lib/gcov: Remove assert(0)

This follows CB:44047 which probably missed this because it's a
custom assert macro (in code that has only recently been added to
build checks).  Without this change, building with gcov fails because
gcc_assert(0) can be build-time verified (as introduced by CB:44044)
while we need runtime failure semantics here.

Change-Id: I71a38631955a6a45abe90f2b9ce3a924cc5d6837
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44105
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/lib/gcov-glue.c

@@ -82,7 +82,7 @@ static int fseek(FILE *stream, long offset, int whence)
 static long ftell(FILE *stream)
 {
 	/* ftell should currently not be called */
-	gcc_assert(0);
+	BUG();
 #if CONFIG(DEBUG_COVERAGE)
 	printk(BIOS_DEBUG, "ftell %s\n", stream->filename);
 #endif