module: Fix KCOV-ignored file name

module.c was renamed to main.c, but the Makefile directive was copy-pasted
verbatim with the old file name.  Fix up the file name.

Fixes: cfc1d277 ("module: Move all into module/")
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/bc0cf790b4839c5e38e2fafc64271f620568a39e.1718092070.git.dvyukov@google.com

kernel/module/Makefile

@@ -5,7 +5,7 @@
 
 # These are called from save_stack_trace() on slub debug path,
 # and produce insane amounts of uninteresting coverage.
-KCOV_INSTRUMENT_module.o := n
+KCOV_INSTRUMENT_main.o := n
 
 obj-y += main.o
 obj-y += strict_rwx.o